DE19608758A1 - Multifunction control valve for hydraulic lifting gear - Google Patents

Abstract

The hydraulic control valve (5) is used with lifting gear. It may select a number of functions including "LIFT", "STOP", "DESCEND", "DAMPING SWINGING MOTION" and "FLOATING". The hydraulic fluid is fed to the two ends of a double-acting hydraulic cylinder or to two opposed cylinders (1,2). The control valve incorporates a rod (6), drilled with a number of passages which may mate up with a variety of different ports in a housing. Springs (8,9) may be used to control the position of the valve rod.

Description

The invention relates to a hydraulic valve arrangement for controlling the functions "lifting", "holding", "lowering", "Vibration damping" and "floating" of the lifting gear of a mobile Working machine according to the preamble of claim 1.

Such a valve arrangement is from the data sheet RE 64 616 / 01.96 "Stabilization module for wheel loaders" der Mannesmann Rexroth GmbH known. On sheet 2/8 is u. a. the Control of the lifting movement of the bucket of a wheel loader shown schematically. The lifting movement is two double Acting lifting cylinder assigned, the piston rods on the Attacking shovel of a wheel loader. The piston rooms and the Rod spaces of the two lifting cylinders are each with each other connected. A hydraulically piloted directional valve controls the Pressure medium flow between a pump, the lifting cylinders and the Tank and thus the functions "hold", "lift" and "lower" of the Bucket of the wheel loader. In addition to these three functions are two further functions "vibration damping" (Stabilization) and "swimming" (floating) provided.

The "vibration damping" function serves to dampen the Nodding vibrations occurring at higher speeds the raised shovel. The pitching vibrations are all the greater the higher the speed of the wheel loader. To dampen the Nodding vibrations therefore occur when a predefinable one is exceeded Minimum speed the "vibration damping" function activated. In the function "vibration damping" are the Piston chambers of the lifting cylinders with one or more hydro save connected, the rod spaces of the lifting cylinders are with connected to the tank. This measure ensures a cavitation-free swinging of the lifting cylinder when driving with raised shovel. The hydraulic accumulators are charged - with the pressure in the piston chambers of the lifting cylinders,  provided that this pressure is greater than the pressure in the lifting cylinders is. The pressure in the hydraulic accumulators is always at least the same large or rather greater than the pressure in the piston chambers of the Lifting cylinder. This ensures that the blade at Activating the vibration damping can not sag. The for the loading of the hydraulic accumulators and the connection of the hydro memory with the piston chambers of the lift cylinder serving valves are combined in a damping module.

The "swimming" function is e.g. B. for leveling with used the bucket lying on the ground in reverse. In this function are the piston chambers and the rod chambers of the Lift cylinders connected to each other and to the tank. The weight the blade displaces pressure medium from the piston chambers of the Lift cylinders in the rod chambers of the lift cylinders and in the tank. If the shovel is not yet on the ground, it sinks after activating the "swimming" function, first from to it comes to rest on the floor.

Since a simultaneous activation of the functions "vibration damping "(with the bucket raised) and" swimming "(with the lowered shovel) are mutually exclusive, is for the Activation of the "vibration damping" function or the function "Float" a hydraulically pilot operated 3-way switching valve provided that from a rest position in two working positions is switchable, one of which has the function "vibration damping "and the other assigned to the" swimming "function is. In the assigned to the "vibration damping" function The 3-way switching valve connects the rods in the working position clear the lifting cylinder with the tank, and the damping module connects the hydraulic accumulators to the piston chambers of the hub cylinder. The hydraulically piloted directional valve for the The functions of "lifting" and "lowering" are located thereby in its rest position assigned to the "hold" function. In the working position assigned to the "swimming" function the 3-way switching valve connects the piston chambers of the stroke cylinders with their rod rooms and with the tank. The  hydraulically piloted directional valve for the control of the Functions "lifting" and "lowering" are in his the rest position assigned to the "hold" function. In the function "Vibration damping" must be from the rod rooms of the hub cylinder displaced pressure medium flow unthrottled to the tank can flow. In the "swimming" function, the must Piston chambers of the lifting cylinder displaced pressure medium flow, the is not picked up by the rod rooms of the lifting cylinders, can also be discharged unthrottled to the tank. The 3-way switching valve is therefore for the accruing To design pressure medium flow. This leads to a nominal size of the 3-way switching valve, the same as that of the hydraulic pilot operated directional control valve. Such switching valves are - ins special compared to valves that only switch from Tax pressures serve - big, heavy and expensive.

The invention has for its object a valve assembly of the type mentioned at the beginning to create the more cost-effective is to be produced.

This object is characterized by those in claim 1 Features resolved. By integrating the functions "Vibration damping" and "floating" in the control piston of the hydraulically piloted directional valve for the functions "Raising", "holding" and "lowering" is for the flow of pressure by means of the functions "vibration damping" and "swimming" no separate 3-way switching valve required. For the Activation of these two functions are sufficient for switching valves Control signals. The hydraulically controlled valve device is Not only is it cheaper to manufacture, it also adds weight saved and it takes up less space.

Advantageous developments of the invention are in the sub claims marked. Since the for the deflection of the Control piston provided control rooms for the control of the Counter pistons are only an additional one Control room for the "vibration damping" function  assigned plunger required. The on the Counter-acting piston ensures a defined position of the counter-piston in control rooms relieved to the tank. The different sized surfaces of counter pistons and Control piston on which when the function is activated "Vibration damping" the control pressures provide for Defined position of the counter piston even if the by opposing side pressures are equal. The "Swimming" function is activated when the control pressure for the "Lower" function exceeds its maximum value. By the use of a second, assigned to the "swimming" function Counter pistons are larger tolerances of the characteristic curve of the Spring arrangement which holds the control piston in the rest position, allowed. Also for the control of the second counter piston only an additional control room is required, since the for the Deflection of the control piston provided control rooms for the Control of the second counter-holding piston can also be used. The spring acting on the second counter piston provides a defined position of the second counter-holding piston to the tank relieved control rooms. The different sized areas of the second counter-holding piston and the control piston to which during the activation of the "lower" function, the control pressures act, ensure a defined position of the counter-piston also if the pressures acting from opposite sides are the same are great.

The invention will be described in more detail below based on two execution shown in the drawings examples explained in more detail. Show it

Fig. 1 shows a first circuit diagram for the control of the lifting mechanism of a mobile machine,

Fig. 2 is a circuit diagram of a stabilization module for the pitching vibrations of a wheel loader,

Fig. 3 shows a second, compared to the shown in Fig. 1 th circuit diagram expanded circuit diagram for the control of the lifting mechanism of a mobile machine and

FIG. 4 shows the circuit diagram of a pilot control device for controlling the hydraulic valve arrangement shown in FIG. 3.

Like parts are in the drawings with the same reference characters.

Fig. 1 shows a circuit diagram for the control of the lifting mechanism of a mobile machine, in particular the shovel of a wheel loader. The piston rods of two differential cylinders 1 and 2 actuate the hoist. The forces exerted by the lifting mechanism on the piston rods of the differential cylinders 1 and 2 are represented by arrows 3 and 4 , respectively. The piston chambers, designated 1 k and 2 k, and the rod chambers, designated 1 s and 2 s, of the differential cylinders 1 and 2 are each connected to one another. A pilot operated directional control valve 5 with a control piston 6 , which is guided in a control block 7 shown only schematically, controls the flow of pressure by means of a pump line P via the directional control valve 5 to the differential cylinders 1 and 2 or from the differential cylinders 1 and 2 a tank line T. The control piston 6 is held in its rest position by a spring arrangement consisting of two coaxially arranged compression springs 8 and 9 between two working positions. The compression springs 8 and 9 are held between two spring plates 10 and 11 , respectively. The spring plate 10 is supported on the control block 7 . The spring plate 11 is supported on a housing 12 which is held on the control block 7 .

A counter piston 13 is arranged in the axial extension of the control piston 6 in a further housing 14 in the axial direction. The housing 14 consists of a guide part 14 f for the counter-holding piston 13 and a screw plug 14 v, which closes the guide part 14 f on the side facing away from the control block 7 . The deflection of the counter-holding piston 13 is limited by the screw plug 14 v on one side and by a stop 14 a of the housing 14 on the other side. The screw plug 14 v and the guide part 14 f of the housing 14 and the abutment piston 13 abutting the stop 14 a enclose a first control space 15 . The side of the counter holding piston 13 facing away from the control chamber 15 and one side of the control piston 6 protrude into a second control chamber 16 which is enclosed by the housing 14 and the control block 7 . The other side of the control piston 6 protrudes into a third control chamber 17 , which is enclosed by the housing 12 and the control block 7 . A spring 18 is arranged between the counter-holding piston 13 and the housing 14 . It ensures that the plunger 13 abuts the stop 14 a of the housing 14 when the control spaces 15 and 16 are relieved of pressure. The surface of the counter-holding piston 13 facing the screw plug 14 v, which is effective for the displacement of the counter-holding piston 13 in the direction of the control piston 6 , is larger than the surface of the control piston 6 in the control chamber 17 which is effective for the displacement of the control piston 6 in the opposite direction.

In addition to the pump line P, which supplies the differential cylinders 1 and 2 with pressure medium, a pump 19 is provided, which supplies the control pressure for the deflection of the control piston 6 of the directional valve 5 . A pressure limiting valve 20 limits the pressure of the pressure medium delivered by the pump 19 from a tank 21 to a pressure p _V which is lower than the pressure of the pressure medium supplied to the differential _cylinders 1 and 2 via the line P. The output of the pump 19 is connected via a control pressure line 22 to two manually operated pressure reducing valves 23 and 24 . They are part of a pilot control unit for hydraulic remote control of directional valves. The output pressure of the pressure reducing valves 23 and 24 is a measure of the deflection of a joystick. Such pilot devices are such. B. in data sheet RE 64553 / 12.94 "Pilot control device with end position locking (type. THF 6, series 2X) for hydraulic remote control of directional control valves" from Mannesmann Rexroth GmbH. Due to the design, only one of the two pressure reducing valves 23 or 24 can be actuated. The respective other pressure reducing valve 24 or 23 is therefore in the rest position shown in FIG. 1, in which the output of the pressure reducing valve is connected to the tank 21 . The output of the pump 19 is also connected via the control pressure line 22 to two electrically actuated switching valves 25 and 26 , which are each shown in the rest position.

The output pressure of the pressure reducing valve 23 is denoted by p _S. It is fed to the control chamber 16 of the directional control valve 5 via a line 27 and controls the "lowering" function. The output pressure of the pressure reducing valve 24 is denoted by p _H. In the rest position of the switching valve 26, it is fed to the control chamber 17 of the directional control valve 5 via lines 28 and 29 and controls the “lifting” function. In the description of the exemplary embodiments, it is assumed that the pressure p _V is limited to 30 bar by the pressure relief valve 20 . A range from 0 to 22 bar of pressure p _{S is} assigned to the "lowering" function and a range of pressure p _H from 0 to 22 bar to the "lifting" function.

The piston chambers 1 k and 2 k of the differential cylinders 1 and 2 are connected to a hydraulic accumulator 33 via a line 30 , a stabilization module 31 and a line 32 . Additional hydraulic accumulators can be connected to the line 32 to increase the storage volume. The stabilization module 31 is also connected to the tank line T. The stabilization module 31 connects the hydraulic accumulator 33 to the piston chambers 1 k and 2 k of the differential cylinders 1 and 2 , respectively, when it is driven by a control signal supplied via an electrical line 34 . Is in the absence of actuation of the stabilization module 31 - if the pressure in the piston chambers 1 k and 2 of the differential cylinder 1 and 2 k higher than the pressure in the hydraulic accumulator 33 is - the hydraulic accumulator 33 to the spaces in the piston 1 k and 2 k ruling Pressure charged.

The structure of the stabilization module 31 is shown schematically in FIG. 2. The electrical line 34 leads to a 2-way switching valve 35 . The control chamber of a 2-way a construction valve 36 is connected via a control line 37 in the rest position of the 2-way switching valve 35 to the output of a sequence valve 38 . If the pressure in line 30 is lower than the connection pressure set on connection valve 38 , the pressure in line 32 is supplied to the control chamber of 2-way cartridge valve 36 . Pressure medium is supplied to the hydraulic accumulator 33 only when the pressure in line 30 is greater than the pressure in line 32 . If, however, the pressure in the line 30 is greater than the set to the sequence valve 38 sequence pressure, the control chamber of the 2-way-A is fed bauventils 36 of the pressure in the conduit 30th The 2-way cartridge valve 35 closes and thereby prevents the hydraulic accumulator 33 from being charged to a pressure which is above the connection pressure of the connection valve 38 . In addition, a pressure relief valve 39 is provided which limits the pressure in the hydraulic accumulator 33 to a maximum pressure adjustable at the pressure relief valve 39 . In the working position of the 2-way switching valve 35 of the control chamber of the 2-way cartridge valve 35 is connected to the tank line T. Since the pressure in the control chamber of the 2-way cartridge valve 35 is thus less than the pressure in line 30 or in line 32 , the 2-way switching valve 35 opens and connects the piston chambers 1 k and 2 k of the differential cylinder 1 and 2 with the hydraulic accumulator 33 .

In the rest position of the control piston 6 of the directional control valve 5 assigned to the "hold" function, no pressure medium flows to or from the differential cylinders 1 and 2 . The pressure in the line 30 is determined by the forces 3 and 4 acting on the piston rods of the differential cylinders 1 and 2 .

When the pressure reducing valve 24 assigned to the “lifting” function is actuated, pressure is supplied to the control chamber 17 , while the control chambers 15 and 16 are relieved of the load on the tank 21 . The control piston 6 of the directional control valve 5 is deflected according to the size of the control pressure p _H against the force of the springs 8 and 9 into the working position assigned to the “lifting” function. The spring plate 10 is supported on the control block 7 , while the spring plate 11 lifts off the housing 12 . The control piston 6 touches the counter-holding piston 13 and displaces it against the force of the spring 18 . Since the counter-holding piston 13 is not acted on by control pressure and the spring 18 is weakly dimensioned, the counter-holding piston 13 sets the control piston 6 practically no resistance. The work area of the control piston 6 assigned to the "vibration damping" function is traversed so quickly that this work area does not come into effect during the transition from the "hold" function to the "lifting" function. If the control piston 6 of the directional control valve 5 is within the working range assigned to the "lifting" function, pressure medium flows from the pump line P into the piston chambers 1 k and 2 k of the differential cylinders 1 and 2 , while pressure medium flows from the rod chambers 1 s and 2 s the tank line T is displaced.

When the pressure reducing valve 23 assigned to the "lowering" function is actuated, pressure is supplied to the control chamber 16 , while the control chambers 15 and 17 are relieved of pressure to the tank 21 . The control piston 6 of the directional control valve 5 is deflected according to the size of the control pressure p _S against the force of the springs 8 and 9 into the working position assigned to the "lowering" function. The spring plate 11 is supported on the housing 12 , while the spring plate 10 lifts off the control block 7 . The springs 8 and 9 are designed so that the control piston 6 moves up to a control pressure p _S of 22 bar within the working position assigned to the "lowering" function. If the control pressure p _S exceeds the limit value of 22 bar, the control piston 6 is deflected further and reaches the working position assigned to the "swimming" function, which follows the working position assigned to the "lowering" function. A pressure point in the pilot control unit enables the operator to recognize that when the control stick of the pilot control unit is deflected further, he leaves the area assigned to the "lowering" function. As long as the control piston 6 of the directional control valve 5 is within the working range assigned to the "lowering" function, pressure medium flows from the pump line P into the rod chambers 1 s and 2 s of the differential cylinders 1 and 2 , while 1 k and 2 k clear from the piston Pressure medium is displaced into the tank line T.

When the control stick of the pilot control device is deflected beyond the pressure point between the areas assigned to the “lowering” and “swimming” functions, the pressure p _S supplied to the control chamber 16 increases to a value which is between 22 bar and 30 bar. The control rooms 15 and 17 are further relieved towards the tank 21 . The control piston 6 is deflected to such an extent that the region of the control piston 6 assigned to the “swimming” function becomes effective. In this position of the control piston 6, the piston chambers 1 and k 2 k and the rod 1 are spaces s and s, the differential cylinders 1 and 2 are connected to each other and in addition 2 to the tank line T. The forces acting on the pistons of the differential cylinders 1 and 2, forces 3 and 4 , respectively, lower the lifting mechanism. The control grooves of the control piston 6 are usually dimensioned in such a way that the lifting mechanism in the "floating" function drops faster than the greatest value of the pressure p _S in the "lowering" function.

The "vibration damping" function is activated when the wheel loader is driving with the bucket raised and a minimum speed of z. B. exceeds 6 km / h. The "vibration damping" function can be activated depending on the driving speed or arbitrarily by the operator of the wheel loader. When driving with the bucket raised, the control stick of the pilot control device is not deflected, ie the pressure reducing valve 23 is in the rest position assigned to the “hold” function and connects the control chamber 16 to the tank 21 . To activate the "vibration damping" function, the switching valves 25 and 26 and the 2-way switching valve 35 of the stabilization module 31 shown in FIG. 2 are switched into the working position. In the working position of the switching valve 25 , the control chamber 15 is acted upon by the pressure p _V. This pressure supports the spring 18 and deflects the counter-holding piston 13 until it abuts the stop 14 a of the housing 14 . In the working position of the switching valve 26 , the control chamber 17 is also pressurized with the pressure p _V. The pressure p _V in the control chamber 17 deflects the control piston 6 in the direction of the counter-holding piston 13 until it bears against it. Since the area of the counter-holding piston 13 acted upon by the pressure p _V is larger than the area of the control piston 6 acted upon by the same pressure, the force with which the control piston 6 presses against the counter-holding piston 13 is less than the force with which the counter-holding piston 13 13 is pressed against the stop 14 a. The control piston 6 is now in the position assigned to the “vibration damping” function. In the working position of the 2-way switching valve 35 is - as described above - the hydraulic accumulator 33 with the pistons 1 k and 2 k of the differential cylinders 1 and 2 connected. In addition, the rod spaces 1 s and 2 s of the differential cylinders 1 and 2 are assigned control grooves of the control piston 6 to the tank 21 via the “vibration damping” function. The "vibration damping" function is effective.

The transition described above in connection with FIG. 1 from the working position of the control piston 6 assigned to the "lowering" function to the working position assigned to the "swimming" function when the pressure p _S exceeds the value of 22 bar assigned to the maximum sinking speed, requires a great deal of effort when selecting springs 8 and 9 . Fig. 3 shows a development of the lifting mechanism control explained with reference to FIG. 1, which allows larger tolerances of the characteristic lines of the springs 8 and 9 . Parts of Fig. 3, which correspond to parts of Fig. 1, are provided with the same reference characters. The springs 8 and 9 are held between a spring plate 10 , which is supported on the control block 7 , and a spring plate 11 ', which is supported on a further counter-piston 40 . The plunger 40 is held in a housing 12 '. The housing 12 'consists of a guide part 12 ' f with a stop 12 'a and a screw plug 12 ' v, which closes the guide part 12 'f. The screw plug 12 'v and the guide part 12 ' f and the abutment piston 40 abutting the stop 12 'a enclose a fourth control chamber 41 . The deflection of the counter-holding piston 40 is limited by the screw plug 12 'v on one side and by the stop 12 ' a of the housing 12 'on the other side. Another spring 42 is arranged between the counter-holding piston 40 and the screw plug 12 'v. It ensures a defined position of the counter-holding piston 40 when the third control chamber 17 and the fourth control chamber 41 are relieved of pressure.

As long as the output pressure p _{S of} the pressure reducing valve 23 is less than 22 bar, a hydraulically operated switching valve 43 acts on the control chamber 41 via a line 44 with the pressure p _V. The pressure p _V supports the force of the spring 41 and presses the counter-holding piston 40 against the stop 12 'a. The counter-hold piston 40 acts as a fixed stop for the spring plate 11 '. The control therefore behaves in the same way as the control shown in FIG. 1.

A spring of the switching valve 43 , designated 43 f, is dimensioned such that the switching valve 43 only switches from the rest position into the working position when the pressure p _{S is} greater than 22 bar. The control piston 6 can deflect the counter holding piston 40 only when the joystick of the pilot control unit is deflected so far in the "lowering" direction that the maximum sink rate associated pressure p _S of 22 bar is exceeded. The pressure p _S is now so great that it switches the switching valve 43 into the working position. In this position of the switching valve 43 , the pressure chamber 41 to the tank 21 is relieved. The pressure chambers 15 and 17 are also relieved to the tank 21 . The pressure p _S , the value of which is between 22 bar and 30 bar, is supplied to the pressure chamber 16 . The spring 42 is dimensioned so weak that the counter-holding piston 40 offers practically no resistance to the control piston 6 . In the deflection of the control piston 6 by the pressure _S p in the control chamber 16 of the counter-retaining piston is displaced so far 40 of the control piston 6 until the counter-retaining piston 40 abuts against the screw plug 12 'v. In addition, the springs 8 and 9 are compressed in accordance with the force acting on the control piston 6 in the axial direction. The control piston 6 is deflected so far that it assumes the working position assigned to the “swimming” function with certainty.

In Fig. 3 the control chamber is supplied to 41 via the switching valve 43 of the pressure p _V. Since the effective surface for the axial displacement of the counter-holding piston 40 of the counter-holding piston 40 in the control chamber 41 is larger than the effective surface for the axial displacement of the control piston 6 of the control piston 6 in the control chamber 16 , it is possible for the control chamber 41 instead of the pressure p _V to supply the pressure p _S. As long as the pressure p _{S is} less than 22 bar, the switching valve 43 is still in the rest position. Due to the different sizes of pressurized surfaces there is a resultant force which presses the counter-holding piston 40 against the stop 12 'a of the housing 12 ' so that the counter-holding piston 40 again serves as a fixed stop for the spring plate 11 '.

FIG. 4 shows the circuit diagram of a pilot apparatus in which the pressure reducing valves are combined with the hydraulically operated shift valve 43 23 and 24. The pilot device is connected to the pump 19 via the line 22 . Line 27 leads to control room 16 , line 28 to control room 17 and line 44 to control room 41 .

Claims (11)

1. Hydraulic valve arrangement for the control of the functions "lifting", "holding", "lowering", "vibration damping" and "floating" of the lifting mechanism of a mobile working machine, which is actuated by at least one double-acting working cylinder, with one of a pilot control unit Control piston pressurized control piston of a hydraulically pilot-controlled directional control valve, at least the functions "lifting", "holding" and "lowering" being controlled as a function of the deflection of the control piston, in particular for controlling the blade of a wheel loader, characterized in that

• - That the control piston ( 6 ) of the directional valve ( 5 ) can be deflected from a rest position assigned to the function "hold" in four working positions,
• - That the control piston ( 6 ) is held by a spring arrangement ( 8 , 9 ) in the rest position between two working positions,
• - That the working positions assigned to the functions "vibration damping" and "lifting" are connected to the rest position of the control piston ( 6 ) in one direction,
• - That connect to the rest position of the control piston ( 6 ) in the other direction, the functions "lowering" and "swimming" assigned working positions and
• - That when activating the "vibration damping" function, a hydraulically controlled counter-piston ( 13 ) limits the deflection of the control piston ( 6 ) to the "vibration damping" function assigned to the working position.

2. Hydraulic valve arrangement according to claim 1, characterized in

• - That the counter-piston ( 13 ) is arranged in an axial extension of the control piston ( 6 ) in a housing ( 14 ),
• - That the housing ( 14 ) and the side of the counter-holding piston ( 13 ) projecting into it from the control piston ( 6 ) form a first control chamber ( 15 ),
• - That the other side of the counter-piston ( 13 ) together with one side of the control piston ( 6 ) is in a common, second control chamber ( 16 ) and
• - That the other side of the control piston ( 6 ) protrudes into a third control chamber ( 17 ).

3. Hydraulic valve arrangement according to claim 2, characterized in that upon activation of the "vibration damping" function, the first control chamber ( 15 ) and the third control chamber ( 17 ) are acted upon by control pressure and the second control chamber ( 16 ) to the tank ( 21 ) is relieved is. 4. Hydraulic valve arrangement according to claim 3, characterized in that in the first control chamber ( 15 ) a spring ( 18 ) between the housing ( 14 ) and the counter-piston ( 13 ) is arranged, which acts in the axial direction on the counter-piston ( 13 ) . 5. Hydraulic valve arrangement according to claim 3 or claim 4, characterized in that the effective for the displacement of the counter-piston ( 13 ) in the axial direction of the counter-piston ( 13 ) in the first control chamber ( 15 ) is greater than that for the displacement of the control piston ( 6 ) in the opposite direction effective surface of the control piston ( 6 ) in the third control chamber ( 17 ). 6. Hydraulic valve arrangement according to one of the preceding claims, characterized in that the "Lower" function a first range of control pressure and "Swimming" function adjoining this area second area of the control pressure is assigned. 7. Hydraulic valve arrangement according to claim 6, characterized in that a second hydraulically controlled counter-piston ( 40 ) limits the deflection of the control piston ( 6 ) as long as the control pressure for the "lowering" function is below the second range assigned to the "swimming" function. 8. Hydraulic valve arrangement according to claim 7, characterized in

• - That the second counter-piston ( 40 ) in the axial extension of the control piston ( 6 ) in a second housing ( 12 ') is arranged displaceably,
• - That the second housing ( 12 ') and in the second housing ( 12 ') projecting from the control piston ( 6 ) facing away from the second counter-piston ( 40 ) form a fourth control chamber ( 41 ) and
• - That the other side of the second counter-piston ( 40 ) protrudes into the third control chamber ( 17 ).

9. Hydraulic valve arrangement according to claim 8, characterized in that upon activation of the "swimming" function, the second control chamber ( 16 ) is acted upon by control pressure and the third control chamber ( 17 ) and the fourth control chamber ( 41 ) to the tank ( 21 ) are relieved . 10. Hydraulic valve arrangement according to claim 9, characterized in that in the fourth control chamber ( 41 ) a second spring ( 42 ) between the second housing ( 12 ') and the second counter-piston ( 40 ) is arranged, which in the axial direction on the second Counter piston ( 40 ) acts. 11. Hydraulic valve arrangement according to claim 9 or claim 10, characterized in that the effective for the displacement of the second counter-holding piston ( 40 ) in the axial direction area of the second counter-holding piston ( 40 ) in the fourth control chamber ( 41 ) is greater than that for the displacement of the Control piston ( 6 ) in the opposite direction effective surface of the control piston ( 6 ) in the second control chamber ( 16 ).