EP0872446B1 - Hydraulic installation for a forklift truck - Google Patents

Description

The invention relates to a hydraulic installation on one Forklift truck with a hydraulic lift drive for a lift, with another hydraulic drive as a tilt actuator as well as with these hydraulic drives individually assigned valve arrangements, by means of those for the different movements of the lift required operating pressures and pressure medium flow rates are controllable, and with the further in the preamble of claim 1, generic Features. Such a hydraulic installation on one Forklift vehicle is known from EP 498610 A.

The linear actuator, by means of whose masses can be raised and lowered must be, which can be up to a few t designed as a single-acting hydraulic cylinder, its lifting operation through valve-controlled pressure medium inflow to Drive pressure chamber and its lowering operation through valve-controlled Outflow of pressure medium from the drive pressure chamber the hydraulic cylinder is controllable. The necessary for this Control valve assembly includes a stroke control valve about the pressure medium from the pressure supply unit can be fed into the drive pressure chamber of the stroke drive cylinder is, as well as a lowering control valve, by means of whose the outflow of pressure medium from the drive pressure chamber of the linear actuator and thus its lowering operation is controllable. The two valves are, their basic function after designed as 2/2-way proportional valves, the one have a blocking basic position and with increasing deflection their valve piston from the basic position flow paths release with increasing flow cross section, whereby between the consumer port of the boost control valve and the drive pressure chamber of the lifting cylinder a check valve is switched by relatively higher Pressure at the consumer connection than in the drive pressure chamber is continuous and otherwise blocking, and between the consumer connection of the lowering control valve and the drive pressure chamber of the linear actuator an unlockable check valve is switched that in the blocking basic position of the lowering control valve is blocking and with whose transition to the flow position is switched.

In an electrically controllable design of these control valves are their valve bodies with the armatures of electromagnet systems coupled with movement and when energized essentially proportional to the excitation current against the Restoring force of valve springs that move the valve body when the magnets are de-energized in the basic position of the valves hold. The energization of the field windings takes place through output currents of an electronic Control unit that this according to setpoint input signals generated, e.g. by hand lever or rotary button actuation of an analog signal generator by a forklift driver can be triggered, the electronic Control unit, however, also in digital format, e.g. at Using a radio remote control can be entered and by means of this into the - analog - excitation currents can be implemented for the field windings of the control magnets.

With such a type of - electrical - control in particular of the lowering control valve must not be opened wide to ensure that in the lowering mode Limits of acceleration and maximum Lowering speed is not exceeded, with it, even if the load to be lowered is great, in everyone Situation there is still a sufficient braking distance available around the lift safely and without the risk of unwanted Bring vibration excitation to a standstill can. In practice, this is achieved in that the electronic Control unit opening the lowering control valve only up to a maximum gap width of the as Throttle lowering flow path allows with the consequence that lowering for relatively small amounts Loads correspondingly low lowering speeds have to be put up with because of the effective Load in the drive pressure chamber of the stroke drive cylinder setting pressure is too low to be at relatively higher Last usable lowering speed to reach can. The disadvantageous consequence of this is that in numerous Cases of lowering operation take place unnecessarily slowly.

Problematic when using valves with proportional solenoids can be controlled, is that this only relatively small travel ranges against relatively high restoring forces enable and are also prone to contamination, whereby as a result the correlation between excitation current and Piston position may be subject to considerable scatter can, i.e. the reproducibility of a piston position relatively poor due to the specification of the excitation current is. In principle, this can counteract this disadvantage be that the piston position by means of a displacement measuring system is monitored and the excitation current is tracked is that the position to be set is also reached however, the effort in this regard is very high and with additional Vulnerability linked.

The object of the invention is therefore a hydraulic installation of the type mentioned at the outset to improve that even with a small amount of a load to be lowered a comparatively high lowering speed can be used is, and that at the same time simple construction of the stroke control valve assembly an increased level of accuracy of adjustment the effective in the raising and lowering operation Flow cross sections is guaranteed.

This object is achieved by the characterizing Features of claim 1 solved.

According to this, the stroke control valve arrangement is a multi-way / 3-position valve trained that has a main piston which by means of an electric servomotor in his various functional positions of the stroke control valve arrangement corresponding positions is movable by positive movement coupling of the valve piston with the Output shaft of the servomotor in a defined relation to the azimuthal positions related to a reference position stand of the rotor of the servomotor, the servomotor is designed as a digitally controllable motor, the Rotor into a digital control signal, e.g. the number a sequence of control pulses, coded azimuthal position its output shaft - forcibly - reached. hereby will, of course, within the increment that due to the digital gradation of the rotor positions is, but can be chosen very fine, a high level of Accuracy and therefore reproducibility of the valve settings reached. A pressure sensor is also provided, that for the pressure in the drive pressure chamber of the stroke drive cylinder characteristic electrical output signals generated, which is fed to an electronic control unit are in accordance with this pressure and thus also load-characteristic output signals of the pressure sensor an automatic limitation of the modulation stroke of the Main piston of the stroke control valve mediated to an amount which is a maximum load and permissible load and The lowering speed of the lift corresponds to below each of which is a dynamically stable, essentially vibration-free operation of the lift is guaranteed is.

A design of the electronic control unit which is expedient for the lowering operation can consist in that, with decreasing load, an increase in the actuation range of the valve piston is permitted, in that the same value of the maximum lowering speed can be used for all loads. Due to the mass dependency of the characteristic frequency ω _{0 of} a hydraulic powertrain, generally by the relationship ω 0 = C m is given, in which the hydraulic stiffness of the drive train is denoted by C and the moving mass is denoted by m, larger speeds and accelerations or decelerations can also be used with decreasing amount of the moving mass.

For precise controllability of the piston deflections Stroke control valve arrangement, it is advantageous if for mechanical Drive coupling of the servomotor and the main piston a non-self-locking gear is provided and the basic position of the main piston by return springs is centered so that the basic position of the piston, which can be monitored by a position encoder, at de-energized motor is taken as it were.

Such a transmission is in a preferred design as Spindle nut drive formed, in which preferably the Spindle as a threaded section of the output shaft of the servomotor is trained and the spindle nut firmly with the Piston connected and preferably in one piece with the piston is executed, which in turn is secured against rotation in the valve housing is slidably guided.

The design of the stroke control valve arrangement provided according to claim 4 with two controllable by deflections of the main piston Seat valves, by means of which the lowering movements the lift is controllable has the advantage that all valve elements of the stroke control valve assembly in a single multi-way three-position valve with a single actuator and a simple one and space-saving construction is achieved.

For the preferred integrated according to claim 5 provided Design of the seat valves in which the valve body of the one seat valve, as it were, the housing of the other seat valve forms, are by the features of claims 6 and 7 structurally simple designs of the two seat valves specified that in the blocking state a hermetically sealed Shutting off the drive pressure chamber of the stroke drive cylinder mediate against the tank space of the stroke control valve.

The pulse-width-modulated solenoid valves provided according to claim 8 for the operation control of further hydraulic drives of the hydraulic installations, for the values of frequencies f _m for the amplitude modulation and for the pulse repetition frequency f _i of "carrier" pulses indicated by the features of claim 9 are from which the amplitude or duration-modulated pulses of the duration T ₁ and T _{2 are} synthesized, have the advantage that from a minimum current of the time-modulated pulses the deflection of the valve body from the respective basic position regardless of the current of the Impulse is, ie only depends on the ratio T ₁ / T ₂ , which in turn can be controlled digitally, with the result that the reproducibility of defined deflections is considerably better in relation to conventional proportional solenoid valves.

By the load comparison circuit provided according to claim 10 is achieved that the highest in the hydraulic installation used operating pressure at the load connection a pressure compensator is pending, the function of which is to given supply pressure constant to the supply oil flow hold.

In a preferred design of the hydraulic installation is for one the housing for the stroke control valve and for the Control valves of the other hydraulic consumers forming Control block a multi-layer structure made of segment sheets provided that they are cohesively connected, are brazed together in practice and with recesses are provided by their contours and Arrangement to each other the cross-sectional shapes and the clear Dimensions of transverse and longitudinal channels as well as valve channels and control chambers within the control block are, which are required to form the cavities mentioned Openings e.g. in a laser cutting process or created using fineblanking or stamping technology are. The manufacture of the control block is therefore essential easier than manufacturing using conventional casting technology. The solder material required for the solder connection can be inserted in segment recesses in a prepared for stacking segment sheet metal in closed cavities form from which the solder passes through the capillary action of the narrow gaps between the segment sheets into the configuration connecting this large area can reach. Pressure (P) supply channels and return channels, to the supply connections of the individual Valves can be easily bypassed of cross channels in which e.g. Sliding valve piston are arranged completely within the housing block be formed. For connection to hydraulic consumers or to the connection piece provided on the pressure supply unit can be designed as prefabricated parts, which are soldered into channel openings of the control block. Compared to those made with conventional casting technology Housings are significant for the control block smaller outer dimensions and also a considerable weight reduction.

Fig. 1

ein Hydraulik-Schaltbild einer erfindungsgemäßen Hydraulik-Installation an einem Gabelstapler-Fahrzeug, bei dem zusätzlich zu einem Hub-Antrieb und einem Neigungs-Stellantrieb auch ein Last-Verschiebe-Antrieb und ein Dreh-Antrieb für die Hebebühne vorgesehen sind;

Fig. 2

eine schematisch vereinfachte LängsschnittDarstellung eines Steuerblocks, der das Gehäuse für das Hub-Steuerventil, eine Druckwaage, ein Rückschlagventil sowie Vergleichsventile der Hydraulik-Installation gemäß Fig. 1 bildet;

Fig. 2a, b und c

verschiedene Funktionsstellungen von Sitzventilen des Hub-Steuerventils gemäß Fig. 2 in einer der Fig. 2 entsprechenden Darstellung und

Fig. 3a bis 3m

schematisch vereinfachte Draufsichts-Darstellungen von Segment-Blechen, aus denen der Steuerblock gemäß Fig. 2 gebaut ist.

Further details of the hydraulic installation according to the invention result from the following description of a special exemplary embodiment with reference to the drawing. Show it:

Fig. 1

a hydraulic circuit diagram of a hydraulic installation according to the invention on a forklift vehicle, in which in addition to a lifting drive and a tilt actuator, a load displacement drive and a rotary drive are provided for the lifting platform;

Fig. 2

a schematically simplified longitudinal sectional view of a control block, which forms the housing for the stroke control valve, a pressure compensator, a check valve and comparison valves of the hydraulic installation according to FIG. 1;

2a, b and c

different functional positions of seat valves of the stroke control valve according to FIG. 2 in a representation corresponding to FIG. 2 and

3a to 3m

schematically simplified top view representations of segment sheets from which the control block according to FIG. 2 is built.

In Fig. 1 is a total of 10, the hydraulic installation a forklift vehicle, not otherwise shown referred to, by means of which loads up to several tons, e.g. with heavy metal parts loaded transport pallets, for storing them Parts of the designated storage spaces of a high-bay warehouse parked or removed from such storage locations can be, the approach to such bearings and the storage of the goods on them or their removal is controlled by such a driver, the forklift "drives" and "controls".

Such a forklift truck, if it is for one Use in closed storage rooms is intended to be a battery powered, electric drive and - also emission-free - hydraulic drives for additional equipment, by means of which the load in the storage position brought and stored there or in the storage position approached and picked up again can.

Accordingly, the hydraulic installation 10 includes the forklift a stroke drive cylinder 11, by means of which one - fork-shaped - lift, which take up the payload can, on a not shown, substantially vertically Move the mast of the forklift up and down can be made to go to predetermined heights of storage floors Raised or picked up from these can.

This stroke drive cylinder 11 is a single-acting linear hydraulic cylinder designed by valve-controlled Pressurization of a drive pressure chamber 12 in In order to raise the lift or the load works and with valve-controlled pressure relief this too Drive pressure chamber 12 by the weight of the piston 13 of the stroke drive cylinder 11 supported load Lowering mediated.

The lifting and lowering movements of this lifting drive cylinder 11 are controllable by means of a stroke control valve 14, which is designed as a three-position directional valve, the one functional position I assigned to the lifting operation, one to the Lowering operation of the stroke drive cylinder 11 assigned Function position II and one of the shutdown of the lifting drive cylinder 11 assigned basic position has 0, the the driver by means of a manually operated direction selector 106, e.g. a pivot lever, can specify wherein the stroke control valve is designed so that when the driver does not operate the direction selector 106 - "lets go" - automatically into the return springs 17 and 18 centered home position 0, in which the stroke drive cylinder 11 is stopped.

Furthermore, the hydraulic installation 10 includes one Inclination adjusting cylinder 19, by means of which in the front area of the vehicle immediately in front of its front axle Lift mast within a limited angular range around a parallel to the front axle of the truck running axle close to the road to the vehicle can be tilted towards or away from the vehicle to thereby also one to the lane or to the storage area of the stored goods downward or upward orientation of the fork of the forklift, i.e. the for that Loading and unloading and good orientations for driving of the mast and the fork. The tilt actuator cylinder 19 is a double-acting linear Hydraulic cylinder designed, the bottom-side drive pressure chamber 21 and its rod-side drive pressure chamber 22 by means of these individually assigned preload valves 23 and 24, which act as pressure relief valves are designed with adjustable pressure limit values, are kept under a minimum pressure.

There is also a lift on the forklift Thrust actuator 26 is provided for moving the load is usable from the fork to the bearing on which the stored goods are to be parked. This thrust drive is also in Fig. 1 by a double-acting represents linear hydraulic cylinder 26.

For the specific exemplary embodiment chosen for explanation is also provided that the lift of the forklift with a low-build, only schematically indicated rotary table 27 is equipped, the by means of a hydraulic one designated 28 overall Rotary drive by at least 180 ° clockwise and counterclockwise is rotatable so that one on the turntable 27 pallets parked in any case in one for parking desired, any orientation is rotatable before them by means of the thrust drive 26 on the respectively provided Storage space is moved.

In the illustrated embodiment, this rotary drive is realized by means of two single-acting linear hydraulic cylinders 28 ₁ and 28 ₂ , which can be actuated by alternative pressurization and relief of their drive pressure chambers 29 ₁ and 29 ₂ arranged on the rod side to drive the rotary table 27 in one or the other direction of rotation , For the drive coupling of the two linear cylinders 28 ₁ and 28 _{2 of} the rotary drive 28, as indicated schematically, a toothed belt 32 which meshes with a gear 31 of the rotary table 27 can be provided, which adjoins the piston rods 30 ₁ and 30 ₂ which run parallel to one another Hydraulic cylinder 28 ₁ and 282 connects to each other and is held in a form-fitting engagement on a 180 ° circumferential area of the gear 31.

To control the movement of the tilt actuating cylinder 19, the Thrust cylinder 26 and the rotary drive 28 are each individually assigned proportional valves 33, 34 and 36 of the same Provided type, which is subsequently based on the Thrust cylinder 26 associated thrust control valve 34 explained becomes:

The thrust cylinder control valve 34 is a linear slide valve trained, the piston, corresponding to the functions mediated by the control valve 34 through a 5/3-way valve symbol 34 'is represented. Corresponding are the valve pistons of the other two control valves 33 and 36 with 33 'and 36' respectively.

A double-stroke magnet system is used to actuate the control valve 34 37 provided, the two by a control connection 38 or 39 represented field windings, in the non-energized state of the piston 34 'of the control valve 34 by the action of preloaded valve springs 41 and 42 occupies its centered center position, which the Home position 0 of the control valve 34 corresponds to the the shutdown of the push cylinder 26 is linked.

Is only the one (a) control winding 38 energized and the other (b) control winding 39 de-energized, the control valve arrives 34 with maximum deflection of its valve piston 34 'against the restoring force of the one, "right" valve spring 42 in its functional position I, the retraction of the Piston rod 43 of the piston 44 of the push cylinder 26 in Direction of arrow 46 is assigned. Will only the other (b) control winding 39 is energized, the control valve arrives 34 with maximum deflection of its valve piston 34 'against the restoring force of the other, "left" valve spring 41 from its basic position 0 to the functional position II, the extension movement of the piston 44 of the thrust cylinder 26 is assigned in the direction of arrow 47.

The same applies mutatis mutandis to the assignment of the functional positions I and II of the control valve 33 to the actuating movements of the piston of the tilt actuating cylinder 19 in alternative directions, and likewise analogously to the assignment of the functional positions I and II of the control valve 36 of the rotary drive 28 to the alternative directions of rotation of the Rotary table 27 corresponding alternative directions of movement of the pistons 44 ₁ and 44 _{2 of} the two single-acting hydraulic cylinders 28 ₁ and 28 _{2 of} the hydraulic rotary drive 28.

The control valve 34 is designed as a so-called pulse-width-modulated proportional valve, in which both the direction and the amount of a deflection of the valve body 34 'in the sense of a transition into the functional position I or the functional position II through the ratio T ₁ / T ₂ of excitation periods T ₁ and T _{2 is} determined, within which only one of the two control windings 38 and 39 is energized, the sum T ₁ + T _{2 of} the period T corresponding to a continuous periodic excitation of both control windings 38 and 39, the pulse repetition frequency f _m of the relationship f _m = 1 / T is given.

A sufficiently high modulation frequency f _m of, for example, 500 Hz, with which the control windings 38 and 39 of the double-stroke magnet system 37 are driven alternately with current pulses of the same current intensity but different pulse durations T ₁ and T ₂ within the period T of the current pulses, is used by the Mechanical inertia of the armature of the double-stroke magnet system 37 and of the valve piston 34 'which is coupled to this in motion, that the reciprocating movements of the armature and the valve piston which occur in time with the modulation frequency f _m only have amplitudes which are small compared to the deflections of the valve piston 34' from it Home position 0, so that the effective deflection from the home position 0 is determined by the ratio of the time periods T ₁ and T ₂ .

The modulation time periods T ₁ and T ₂ are set by summing processing of clock pulses of constant, short duration, the pulse repetition frequency f _{i of} these clock pulses being 50 to 100 and higher than the pulse width modulation frequency f _m , which corresponds to the relationship f _m = 1 / ( T ₁ + T ₂ ) is sufficient.

In this type of electrical valve control, moving to the basic position 0 of the valve 34 corresponds to the approximation of the respective pulse duration ratio T ₁ / T ₂ to the value 1; a transition to the functional position I and within this the use of increasing flow cross-sections of the released flow paths takes place by controlling values of the excitation-time ratio T ₁ / T ₂ which are greater than 1 and become increasingly larger, while a transition to the functional position II and within this the use of increasing flow cross sections takes place by controlling values of the ratio T ₁ / T ₂ which are smaller than 1 and decrease further. It is expedient here if the ratio T ₁ / T ₂ between extreme values of 100/1 and 1/100 can be varied and the entire modulation range is divided into approximately 100 incremental steps, so that a sufficiently finely graduated setting of the valve piston deflections is achieved ,

The control valve 34 is hydraulic in terms of achievable Pipe connections a 5/3-way valve that a pressure (P) supply connection 48 on the supply side has, via a pressure supply line 49 to the pressure outlet 51 of the pressure supply unit, designated overall by 52 connected, a return (T) connection 53, which is connected via a return line 54 the reservoir 56 of the pressure supply unit 52 connected and a load (x) sensing connector 57 associated with one of the connected consumers 26 Inlet port 58 of a shuttle valve 59 connected is, depending on whether the load sensing connection 57 prevailing pressure is lower or higher than the pending at the other inlet connection 61 of the shuttle valve 59 Pressure the load sensing port 57 of the control valve 34 blocks against the output 62 of the shuttle valve or connects to the output 62 of the shuttle valve 59.

On the consumer side, the control valve 34 has an A consumer connection 63, the one with the bottom-side drive pressure chamber 21 of the push cylinder connected as a consumer 26 is connected, and a B consumer connection 64, the with the rod-side drive pressure chamber 22 of the thrust cylinder 26 is connected.

The consumer connections are in the basic position 0 of the control valve 34 63 and 64 against each other and against Supply connections 48 and 53 blocked, but is the T-return port 53 "internal" with the load (x) sensing port 57 connected. In the retreat of the Piston 44 of the thrust cylinder 26 assigned functional position I is the pressure supply port 48 of the valve 34 connected to its B consumer connection 64 and internally with the load sensing connection 57, which is now against the return port 53 is blocked, which in turn is connected to the A consumer terminal 63. In this Function position I flows pressure medium from the pressure supply line 49 via a between this and the P supply connection 48 of the valve 34 switched check valve 66, which in this functional position is in its open position reaches the rod-side drive pressure chamber 22 of the thrust hydraulic cylinder 26, while from the bottom Drive pressure chamber 21 pressure medium via the control valve 34 to the reservoir 56 of the pressure supply unit 52 flows.

In the associated with the feed operation of the thrust cylinder 26 Functional position II of the control valve 34 is the latter Pressure (P) supply connection 48 with the A consumer connection 63 and with the load sensing connection 57 of the Control valve 34 connected and against the T-return port 53 blocked off, which is now connected to the B consumer connection 64 is connected via the pressure medium from the rod side Pressure chamber 22 of the pressure cylinder can flow out during the bottom-side drive pressure chamber 21 under high pressure Media flows in.

The type of control of rotary movements of the turntable 27 by means of the control valve assigned to the rotary drive 28 36 is the same as explained with the thrust actuator 26, where in the illustrated explanatory example Load (x) sensing port 57 of the rotary actuator control valve 36 with the second inlet connection 61 of the push cylinder 26 associated shuttle valve 59 is connected.

In the event that both the rotary drive 28 and the thrust cylinder 26 are activated, the shuttle valve 59 provides a comparison of the drive pressures in the respective pressurized drive pressure chamber 21 or 22 or 29 ₁ or 29 _{2 of} the thrust cylinder 26 or the rotary drive hydraulic cylinder 28 ₁ or 28 ₂ and thus a load comparison, the higher of these two operating pressures being present at the output 62 of the shuttle valve 59.

The output 62 of this "comparison" shuttle valve 59 is with the one inlet connection 67 of a further "comparison" shuttle valve 68 connected to the tilt actuator 19 is associated with the second inflow port 69 of this shuttle valve 68 with the load sensing connection 57 of the tilt control valve 33 connected is.

In contrast to the control valves 34 and 36 for the thrust cylinder 26 and the rotary drive 28, the pressure (P) supply connection 48 of the tilt control valve 33 is connected directly to the pressure supply line 49, which is connected to the pressure outlet of the pressure supply unit 52; however, a nonreturn valve 70 ₁ and 70 _{2 is} connected between the A consumer connection 63 of the tilt control valve 33 and the rod-side drive pressure chamber 22 of the tilt actuating cylinder 19 and between the B consumer connection 64 and the bottom drive pressure chamber 21 of the tilt actuating cylinder 19 , which is blocking at higher pressure in the respective drive pressure chamber 22 or 21 than at the associated consumer connection 63 or 64, so that a set mast inclination is reliably maintained even when the inclination adjusting cylinder 19 is stopped and does not change under the mast's own load can. By means of the preload valves 23 and 24, which are individually connected in parallel with the two non-return valves 70 ₁ and 70 ₂ , minimum pressure values are determined and can be preset, which, when the mast inclination changes, in that of the drive pressure chambers 21 and 22 of the inclination actuating cylinder 19 are maintained from which pressure medium must flow to change the position.

Also associated with the single-acting stroke drive cylinder 11 Stroke control valve 14 is, in functional analogy to the other consumers 19, 26 and 28 of the hydraulic installation 10 associated control valves 33, 34, and 36, designed as a 5/3-way proportional valve.

The stroke control valve 14, as well as that for the others Consumers 19, 26 and 28 provided control valves 33, 34 and 36, a pressure (P) supply connection on the supply side 48, with the pressure supply line 49 communicating directly, a return (T) connector 53, which communicates directly with the return line 54 is connected, and a load (x) sensing terminal 57, the one with the inlet connection 71 of a functional the shuttle valves 59 and 68 corresponding others Shuttle valve 72 is connected, and, consumer side, a B consumer port 64 that is direct communicating with the drive pressure chamber 12 of the stroke drive cylinder 11 is connected, and an A consumer connection 63, the to the drive pressure chamber 12 of the stroke drive cylinder 11 is connected via a check valve 73, which by relatively higher pressure at the A consumer port 63 of the control valve 14 than its B consumer connection 64 Flow position assumes and is otherwise blocking.

In the basic position 0 of the stroke control valve 14 there are A and B consumer connections 63 and 64 and its Pressure (P) and return (T) connections 48 and 53 against each other blocked, but the return (T) connection 53 and the Last (x) sensing terminal 57 "internally" connected together.

In the functional position I of the stroke control valve 14, the associated with the upward movement of the lift of the forklift the pressure (P) supply port 48 is the A load terminal 63 and the load (x) sensing terminal 57 of the stroke control valve 14 communicating with each other connected, but against its return (T) connection 53 and its B consumer connection 64 blocked.

In the lowering operation of the lifting drive cylinder 11 assigned functional position II of the stroke control valve 14 are the B-consumer connection 64, the return (T) connection 53 and the load (x) sensing port 57 of the stroke control valve 14 communicating with each other, but against its A consumer port 63 and its pressure (P) supply port 48 cordoned off in this working position II are blocked off from each other.

The second inlet port 74 of the one with the load sensing port 57 of the stroke control valve 14 connected on one side Shuttle valve 52 is connected to the outlet 76 of the tilt control valve 33 associated shuttle valve 68 connected.

The output 77 of the stroke control valve 14 assigned Shuttle valve 72 is one with the load pressure connection 78 Two-way pressure compensator 79 connected, its reference pressure connection 81 to the pressure outlet 51 of the pressure supply unit 52 is connected, from which the pressure supply line 49 to which the pressure (P) supply connections 48 of the individual control valves 14, 33, 34 and 36, partly via the check valves 66, connected are.

A pressure relief valve 83 is located between the load pressure connection 78 of the pressure compensator 79 and the return (T) connection 82, from which the return line 54 starts, which is connected to the respective return connections 53 of the control valves 14, 33, 34 and 36 switched, which limits the operating pressure with which the individual drives 11, 19, 26 and / or 28 can be acted upon, to a predeterminable adjustable maximum value P _max of 100 bar.

The piston represented by the 2/2-way valve symbol 84 of the pressure compensator 79 forms with its opposite one another schematically indicated end faces 86 and 87 same effective area the axially movable pressure-tight Limits of an operating pressure chamber 88, in which the Load pressure connection 78 of the respective operating pressure is coupled which is activated when one of the drives is activated Actuation of its control valve and a reference pressure chamber 89, in via the reference pressure connection 81 the outlet pressure of the hydraulic pump 91 of the pressure supply unit 52 is coupled, which means of an electric drive motor 92 is driven and in operation with a substantially constant delivery rate is working.

Through an arranged within the load pressure chamber 88, preloaded balance spring 93, the preload of a pressure from e.g. 3 bar is equivalent, the piston 84 is the Pressure compensator 79 pushed into its locked position. For the Case that none of the drives 11, 19, 26 and 28 is activated and thus the load pressure chamber 88 is depressurized, the Pressure compensator due to the effect of the reference pressure chamber 89 coupled output pressure of the pump 91 in their Flow position I and thus works in circulation, in the hydraulic medium from the pump 91 via the pressure compensator 79 is conveyed back into the storage container 56, whereby - because of the effect of the balance spring - above the pressure balance there is a pressure drop of 3 bar.

For setting actuation of the stroke control valve 14, to the structural and functional explanation 2 is a backlash-free, non-self-locking, a total of 94 designated spindle drive provided the one by means of a pulse-controlled electric motor 96, e.g. a stepper motor can be driven in rotation Threaded spindle 97 and one in meshing with this Engaged spindle nut 98 which is fixed to the Valve piston 14 'of the stroke control valve 14 is connected, the by means of a housing-fixed, radial pin 95, the protrudes into a longitudinal groove 99 of the piston against rotation is secured within a housing bore 101 and in this can nevertheless be easily moved axially back and forth is led.

The electromotive actuating device explained so far 94, 96 of the stroke control valve 14 enables one very fine "digital" graded adjustment of the deflections of the piston 14 'of the stroke control valve 14 compared to that Standstill of the lift assigned to the middle position as Home position 0, for recording an electronic 102 or electromechanical reference signal generator provided is the one for the - spring centered - middle position of the Piston 14 'characteristic electrical reference signal to one provided to control the stepper motor 96 outputs electronic control unit 103, based on which the electronic control unit 103 automatically detects when the piston 14 'is in the basic position 0 or this goes through.

To explain the electronic control unit 103 considered it sufficient based on their functions to describe, if known, a specialist in electronic Circuit and control technology without further ado is able to control the electronic control unit 103 and their periphery with the functions to be explained now to realize.

The electronic control unit 103 is supplied with electrical output signals of a setpoint specification unit 104 ₁ as information inputs, by actuating them, for example by means of a hand lever 106 which can be pivoted back and forth, the forklift driver corresponds to the setpoint signals corresponding to the driver's request with regard to the operating mode - raising or lowering Hoist drive cylinder 11 and in terms of the speed at which the lifting or lowering operation is to take place.

To control setting angles, feed forces and / or orientation angles, individually assigned setpoint specification units 104 ₂ , 104 ₃ and 104 _{4 are} provided for the tilt actuator 19, the thrust drive 26 and the rotary drive 28, which, analogously to that for the Control of the lifting and lowering operation of the setpoint specification unit 104 ₁ provided can be actuated by means of a separate hand lever 106 or a rotary knob 106 ', the setpoint output signals of the individual setpoint specification units 104 ₁ to 104 _{4 of} the electronic control unit 103 being at a separate setpoint -Inputs 109 ₁ to 109 _{4 are} fed.

Another input for information is the electronic one Control unit 103 the electrical output signal of a electronic or electromechanical pressure sensor 107 fed that is a direct measure of that in the drive pressure chamber 12 of the stroke drive cylinder 11 prevailing operating pressure and therefore also a measure of the load, which means the lift of the forklift raised or lowered shall be.

From processing this information input, e.g. by comparison with permanently stored data pairings or combinations are determined by the electronic control unit 103 for controlling the lifting and lowering operation of the Stroke drive cylinder 11 that deflection stroke of the piston 14 'of the stroke control valve 14, which is required to for a given amount of load based on the output signal of the pressure sensor 107 is detected, the desired one Set lifting or lowering speed and generated the number of drive pulses required for this deflection stroke for the stepper motor 96, that per drive pulse makes a rotation by an incremental angular amount, due to the design of the spindle drive 94 an incremental axial displacement path of the piston 14 ' of the stroke control valve 14 corresponds, so that by the number the output from the electronic control unit 103 Control pulses - digital - the deflection stroke of the Piston 14 'is precisely specified by which the piston 14' is relative to the basic position 0 in the sense of taking the functional position I or II of the control valve 14 are moved got to.

This function of the electronic control unit 103 is particularly important for the lowering operation of the lifting platform, in which only the load supported on the piston 13 of the lifting drive cylinder 11 is effective for developing the pressure which conveys the return flow of the hydraulic oil to the reservoir 56, so that it is around To achieve a certain lowering speed with a comparatively low load, it is necessary to control a larger flow cross-section of the flow path 108 of the control valve 14 which is effective in the lowering operation than with a comparatively higher load, under which a higher pressure results in the drive pressure chamber 12, which is already at lower flow cross-section of the flow path 108 of the control valve used in the lowering mode (and correspondingly stronger throttling effect of the same) is sufficient to achieve a lowering speed preselected by the setpoint specification unit 104 ₁ .

Based on the load-characteristic output signal of the Pressure sensor 107 is also a load-appropriate acceleration, Driving and braking operation of a not shown electric driving motor of the forklift possible, in particular such that comparatively lower at high load Acceleration values can be set as compared to low load and / or also at high load maximum driving speed is reduced.

The electronic control unit 103 also generates the relatively high-frequency control pulse sequences required for the operation control of the tilt control valve 33, the thrust control valve 34 and the rotary control valve 36 for their double-stroke magnet systems 37, as well as control signals for the battery-powered drive motor 92 the high pressure pump 91 of the pressure supply unit 52, by means of which the delivery rate can be controlled as required. Such control is expediently carried out in such a way that the hydraulic drive circuits controlled by one of the control valves 14, 33, 42 and / or 36, which are represented by the respective drive cylinders 11, 19, 26 and 28 ₁ and 28 ₂ , can work in a dynamically stable manner , however, to keep the hydraulic oil flow that flows through the pressure compensator 79 to the reservoir 56 in the control mode at the lowest possible value in order to keep the power loss caused by this circulating oil flow as low as possible. Such a type of speed or power control of the electric drive motor 92 is possible in the exemplary embodiment selected for explanation at least for the lifting and lowering operation of the lifting drive cylinder 11, in which the operating pressure prevailing in the drive pressure chamber 12 is monitored by means of the pressure sensor 107.

To explain structural details of the stroke control valve 14 that in terms of its principal function has already been explained with reference to FIG. 1, is now referred back to Fig. 2, the the linear actuator 11 assigned part of a total designated 110 Control block shows in which the stroke control valve 14th and the pressure compensator 79 are integrated, as well as the check valve 73, which is between the A consumer connection 63 of the stroke control valve 14 and the drive pressure chamber 12 of the Hub drive cylinder 11 is switched, as well as the stroke control valve 14 assigned shuttle valve 72 and that too Shuttle valve 68, which is used to sense the operating pressure on the inclination control valve not shown in FIG. 2 33 is provided. This control valve 33 and the further control valves 34 and 36 can be added to the one for the stroke control valve 14 shown in an analogous manner in the Control block 110 may be integrated.

The arrangement of the stroke control valve 14 and the pressure compensator 79 and the check valve 73 is taken so that their central longitudinal axes 111 and 112 and 113, along which their pistons can be pushed axially back and forth, as well the central longitudinal axes 114 and 116 of the P supply connection 48 or the T return connection 59 in the longitudinal median plane marked by the plane of the drawing of the control block 110.

Between a block-shaped housing part 117, which is arranged on the same side of the control block 110 as the supply connection pieces 48 and 53, and forms the housing-fixed boundary of an annular pressure-tightly closed B-consumer connection chamber 118, which is connected via the B-consumer connection 64 of the stroke Control valve 14 is in communicating connection with the drive pressure chamber 12 of the stroke drive cylinder 11, and a block-shaped housing part 117 arranged opposite this block-shaped housing part 119, which also forms a block-shaped housing part 119, which forms the housing-fixed boundary of a pressure-free tank connection chamber 121 which is connected to the T-return connection 53 is kept in a constantly communicating connection and receives the spindle drive 94, by means of which the piston 14 'of the stroke control valve 14 can be pushed axially back and forth, the control block 110 has a multilayer structure made of hard-soldered segment sheets hen 122 ₁ to 122 ₁₄ , which are arranged in the order of their indices one above the other or side by side with their soldered boundary surfaces perpendicular to the plane of the central longitudinal axes 111 to 114 and 116 between the block-shaped housing parts 117 and 119.

The segment sheets 122 ₁ to 122 ₁₄ are provided with punched-out and / or, for example, cut-outs in a laser cutting process, the shape of the contours and, if necessary, the coaxial arrangement of each other, predetermine cross-sectional shapes and clear dimensions of transverse and longitudinal channels within the control block 110.

According to the supervisory representations of Segementbleche 122 _{1-122 14} shown in FIGS. 3a to 3m, the segment plates are provided 122 _{1-122 8} with circular holes 123 ₁ to 123 ₈ of the same diameter, which form a cross-channel 123 in mutually aligned arrangement, in the connection socket 48 'of the pressure (P) supply connection 48 is soldered.

This transverse channel 123 opens into a longitudinal slot 124 of the ninth segment plate 122 ₉ , which together with the segment plates 122 ₈ and 122 _{10 forms} the pressure supply line 49 (FIG. 1), which connects to the pressure (P) supply connections 48 of the individual control valves 14 , 33, 34 and 36 is connected.

The eighth segment plate 122 ₈ and the tenth segment plate 122 ₁₀ , between which the pressure (P) supply line 49 runs, as well as the twelfth segment plate 122 ₁₂ and the 14th

Segment sheet 122 ₁₄ are provided in a coaxial arrangement with respect to the central longitudinal axis 111 of the stroke control valve 14 with circular, mutually aligned, smoothed through post-processing recesses 126 ₈ , 126 ₁₀ , 126 ₁₂ and 126 ₁₄ , the sliding seats for radial flanges 127, 128 and 129 by means of of the stepper motor 96 form axially displaceably drivable valve piston 14 ', by means of which the piston is mounted in the part of the control block 110 which forms the valve housing and is pressure-tight and axially smoothly displaceable.

The segment sheets 122 ₁ to 122 ₅ are provided in a coaxial arrangement with respect to the central longitudinal axis 116 of the T return connection 53 with further circular recesses 131 ₁ to 131 ₅ which are aligned with one another and form a transverse channel 131 into which the connecting piece 53 'of the T -Return connection is soldered. This transverse channel 131 opens into the return line 54 which runs between the fifth segment plate 122 ₅ and the eighth segment plate 122 ₈ in the exemplary embodiment shown and which extends on the one hand to the return connection region of the stroke control valve 14 and further bypasses the transverse channel 123 by - not shown - continues the area of the control block 110, in which the return connections 53 of the further control valves 33, 34 and 36 are located. The shape of the recesses 132 ₆ and 132 _{7 of} the segment sheets 122 ₆ and 122 ₇ , which between the segment sheets 122 ₅ and 122 _{8 determine} the shape of the part of the return line 54 which extends from the transverse channel 131 to the region of the stroke control valve 14, is selected that with the central longitudinal axis 111 of the stroke control valve concentrically curved edge areas 133 ₆ and 133 _{7 of} the return line recesses 132 ₆ and 132 _{7 of} the two segment plates 122 ₆ and 122 ₇ at a significant radial distance from the edge of the sliding seat opening 126 _{8 of} the segment plate 122 ₈ run in which the piston flange 127 is slidably sliding, which is arranged on the side of the valve piston 14 'facing away from the drive motor 96, and that the circular mouth edges 134 ₅ and 134 ₈ (FIG. 2), over the mutually aligned transverse channels 136 and 137 of the control block 110 to the through the recesses 132 ₆ and 132 ₇ of the segment plates 122 ₆ and 122 ₇ edged portion of the R Connecting the return line 54, to completion of this retrace line portion within the clear dimensions. In this case, the one transverse channel 136 is formed by circular openings 136 ₂ , 136 ₃ , 136 ₄ and 136 _{5 of} the segment sheets 122 ₂ to 122 ₅ which are aligned with one another and is closed on the outside in a pressure-tight manner by a stopper 138 which is in one with the common central longitudinal axis 112 of the segment sheet -Openings 136 ₂ to 136 ₅ coaxial recess 136 ₁ slightly larger diameter of the segment plate 122 _{1 is} fixed.

The other transverse channel 137 is formed by aligned circular openings 137 ₈ and 137 ₁₀ to 137 _{14 of} the segment sheets 122 ₈ and 122 ₁₀ to 122 ₁₄ and is closed on the outside by another, block-shaped, side housing end part 139 pressure-tight to the outside.

The segment sheets 122 ₁ and 122 ₃ to 122 ₁₀ are provided with circular recesses 141 ₁ and 141 ₃ to 141 ₁₀ , which are arranged coaxially with respect to the central longitudinal axis 113 of the check valve 73, which is between the A consumer port 63 of the stroke control valve 14 and the drive pressure chamber 12 of the stroke drive cylinder 11 is switched.

The second segment plate 122 ₂ arranged between the segment plates 122 ₁ and 122 ₃ has a recess 141 ₂ which has an edge region 142 which is coaxially curved with the central axis 113 of the check valve 73 and an edge region 143 which is coaxially curved with the central longitudinal axis 111 of the stroke control valve 14 The radius of the curvature coaxial with the central axis 113 of the check valve 73 is slightly larger than that of the adjacent circular recesses 141 ₁ and 141 _{3 of} the segment plates 122 ₁ and 122 ₃ and the radius of the with the central longitudinal axis 111 of the stroke control valve 14 coaxially curved wheel region 143 of this recess 141 _{2 is} significantly larger than that of the other curved edge region 142 and also somewhat larger than the radii with the central longitudinal axis 111 of the stroke control valve 14 of coaxially arranged recesses 144 ₁ , 144 ₃ and 144 ₄ and 144 ₄₅ of essentially the same diameter of the segment sheets 122 ₁ , 122 ₃ as well as 122 ₄ and 122 ₅ , which in turn border a transverse channel 144 which is open towards the housing part 117 and into which the housing part projects with a sleeve-shaped extension 146, the diameter of the circular recess 144 _{4 of} the segment plate 122 ₄ for receiving an annular seal 147 being somewhat larger is the diameter of the "large" circular recesses 144 ₁ , 144 ₃ and 144 _{5 of} the segment plates 122 ₁ , 122 ₃ and 122 ₅ which are aligned with one another and which are identical with regard to their recess image.

The curved edge regions 142 and 143 of the recess 141 _{2 of} the segment plate 122 ₂ , which overlap with the recesses 141 ₁ and 141 ₃ and the recesses 144 ₁ and 144 _{3 of} the segment plates 122 ₁ and 122 ₃ , each close with a smooth curvature and rectilinear edge regions 148 of the recess 141 ₂ .

The housing channel which is kept free by the recess 141 _{2 of} the segment plate 122 ₂ and which extends between the B-consumer connection chamber 118 of the stroke control valve 11 and the connection channel coaxial with the central longitudinal axis 113 of the check valve 73 forms, as it were, the B-consumer connection 64 of the stroke control valve 14 ,

The transverse channel coaxial with the central longitudinal axis 113 of the check valve 73, designated overall by 141, has in the central region of the control block 110 a conical taper forming the valve set 149 for the valve body 151 of the check valve 73 shown in the shape of a truncated cone, with which it connects to the A-consumer connection channel 63 connects, which is formed by the mutually aligned recesses 141 ₇ to 141 _{10 of} the segment plates 122 ₇ to 122 ₁₀ .

The A-consumer connection channel 63 opens into a "flat" -eliptically bordered recess 126 _{11 of} the eleventh segment plate 122 ₁₁ , which, depending on the functional position of the piston 14 'of the stroke control valve, either via a throttle gap opened in the valve is connected to the pressure supply line 49 and is blocked off from the T return line 54 or is connected to it and is blocked off from the pressure supply line 49. This elliptically bordered recess 126 _{11 of} the segment plate 122 _{11 also} mediates the communicating connection of the A consumer connection 63 of the stroke control valve 14 to its load sensing connection 57 (FIG. 1).

The recess 132 ₇ bordering part of the return line 54 of the segment plate 122 ₇ arranged approximately at the level of the valve seat 149 has a recess 141 ₇ , the edge of which forms part of the valve seat 149, with a radially spaced arcuate bulge 153 with a transverse channel 154, the central longitudinal axis 156 of which runs parallel to the central longitudinal axes 113 and 111 of the check valve 73 and the stroke control valve 14 and in their plane, is in communicating connection. This transverse channel 154 is formed by circular openings 154 ₈ to 154 _{12 of} the segment plates 122 ₈ to 122 ₁₂ which are aligned with one another; it also communicates with a "tank space" recess 126 _{13 of} the segment plate 122 ₁₃ , which has an arcuate border area with the central longitudinal axis 111 of the stroke control valve 14 and an opening area 157 extending from it, and a slot-shaped bulge 158 extending therefrom, within the end section of which the transverse channel has 154 opens into the overall keyhole-shaped recess 126 _{13 of} the segment plate 122 ₁₃ . The radius of curvature of the arcuate opening edge region 157 'of the tank space recess 12613 is somewhat larger than the radius of the sliding fit recesses 126 ₈ , 126 ₁₀ , 126 ₁₂ and 126 ₁₄ , in which the piston 14 is coaxial with the central longitudinal axis 111 of the stroke control valve 14 'With its piston flanges 127, 128 and 129 is slidably arranged so that between the 12th and the 14th segment plate 122 _{12 there is} an annular space 159 which extends over the slot-shaped bulge 158 of the tank space recess 126 ₁₃ , the transverse channel 154 and the arcuate curved bulge 153 of the "tank" recess 132 _{7 of} the segment plate 122 ₇ with the T-return line 54 is in constantly communicating connection. This also applies to the tank connection chamber 121 of the stroke control valve 14, which has a transverse bore 161 of the coupling section of the piston flange 129 protruding into this chamber 121, a longitudinal bore 162 of the valve piston 14 'communicating therewith, and again with the longitudinal bore 162 is in communicating connection with the transverse bore 163, which is arranged between the piston flange 129 and the central piston flange 128 on a piston rod section 164 connecting them, is communicatively connected to the annular space 159.

Further recesses which are provided on the segment sheets 122 ₁₁ to 122 ₁₂ , as far as shown in FIGS. 2 and 3j to 3m, are the following:

The segment plate 122 ₁₂ is provided with a circular opening 166 which is small in diameter and which forms the one inlet connection 71 of the shuttle valve 72 which is provided on the stroke control valve 14 for load comparison. The 14th sheet segment 122 ₁₄ is provided with a recess 167 of somewhat larger diameter, which is coaxial with the aforementioned recess 166 and into which a valve sleeve 168 is inserted in a pressure-tight manner, which forms the second inlet connection 74 and the valve seat of the shuttle valve 72 opposite the first inlet connection 71. The outlet 77 of this shuttle valve 72, which is connected to the operating pressure chamber 88 of the pressure compensator 79, is formed by a bulge 169 of the largely round recess 137 _{13 of} the segment plate 122 ₁₃ which is coaxial with the central longitudinal axis 112 of the pressure compensator and which also extends to the valve space extending between the valve seats of this valve limited.

The segment plate 122 ₁₂ is provided with a further “small”, circular recess 171, which forms the one inlet connection 69 of the shuttle valve 68, which is connected to the load sensing connection 57 of the tilt control valve 33. A connection channel required in this regard is represented by the recess 172 of the segment plate 122 ₁₁ .

In the recess 171 of the segment plate 122 ₁₂ coaxial, the diameter slightly larger recess 173 of the segment plate 122 ₁₄ , a valve sleeve 174 is inserted in a pressure-tight manner, which forms the inlet connection 67 of the change-over valve 68 associated with the inclination control valve 33 and one of its two valve seats.

A substantially slot-shaped recess 176 of the segment plate 122 ₁₃ forms with a curved area coaxial with the recess 171 of the segment plate 122 ₁₂ the boundary of the space of the shuttle valve 68 which extends between the valve seats and which is assigned to the inclination control valve 33 and mediates the communicating connection of the valve outlet 76 with a circular connection recess 177 of the segment sheet 122 ₁₄ from which a connection channel leads to the second inlet connection 74 of the shuttle valve 72 assigned to the stroke control valve. With these openings 176 and 177 with respect to the connection of the shuttle valve 59, which is no longer shown in FIG. 2 and is assigned to the linear actuator, functionally analogous recesses in the segment plates 122 ₁₃ and 122 ₁₄ are designated 176 'and 177' in FIGS. 31 and 3m.

For further structural and functional explanation of the Stroke control valve 14, which in FIG. 2 in its load-lifting operation assigned functional position I shown is now also supplementary to FIGS. 2a, 2b and 2c Referenced in which the various functional positions I, 0 and II of the stroke control valve 14 assigned Functional positions of a total designated 14 '' Lowering valve unit in relation to the different ones Positions of the positions assigned to Main piston 14 'are shown.

The lowering valve unit 14 '' can be preassembled Assembly of the stroke control valve 14 in the housing part 117 integrated on the side of the multi-layer control block 110 is attached and against this by means of the seals 147 and 178 and with another ring seal 179 is sealed in the area of the consumer Connection piece 181 is arranged, which is also on the Housing part 117 is arranged.

Within this housing part 117, which is the limit fixed to the housing which forms B consumer connection chamber 118 this through an intermediate wall 182 against an outer Deposed pressure chamber 183, which in turn by means of a assembly reasons necessary screw plug 184 is completed pressure-tight to the outside. This partition 182 has one with the central longitudinal axis 111 of the Stroke control valve 14 coaxial, central bore 186, in the a cylindrical-pot-shaped "outer" valve body 187 is slidably arranged in a pressure-tight sliding manner.

The diameter D1 of this central partition wall bore 186 is slightly larger than the diameter D2 one with this coaxial tank compartment side opening 188 of the housing part 117 formed by an inner annular rib 189 of the sleeve Extension 146 of the housing part 117 is edged, through which the B-consumer connection chamber 118 against the Tank chamber 54 'is offset by the in the area of Stroke control valve 14 extending portion of the return line 54 is formed. The edge of the connection chamber 191 of the opening 188 bordered by the annular rib 189 forms a circular valve seat for the cup-shaped Valve body 187 with a circular cone Sealing surface 192, over which an outer cylindrical outer surface 193 to the bottom area 194 of the valve body 187 connects, can be supported on the valve seat 191.

The valve body base 194, whose tank space-side boundary surface 196 extends radially within the conical sealing surface region 192 at right angles to the central longitudinal axis 111 and whose inner boundary surface 197 in the central bottom region near the axis also extends at right angles to the central longitudinal axis 111, has a central opening 198 in this region, the diameter of which d _{1 is} significantly smaller than the inner diameter d _{2 of} the nevertheless relatively thick-walled cylinder jacket 199 of the cup-shaped valve body 187.

The inner circular edge 201 forms the seat for a dome-shaped or frustoconical as shown Sealing body 202 of a second valve body 203 of the lowering valve unit 14 ″, which acts as a stepped piston is formed with its larger diameter Piston stage 204 against the inner lateral surface 206 of the Cylinder jacket 199 of the cylindrical pot-shaped valve body 187 is slidingly sealed. This outside cylindrical Piston stage 204 is in turn cylindrical-pot-shaped, being in communication with the outer pressure chamber 183 Connected interior 207 via a longitudinal channel 209 axially penetrating bottom region 208 and communicating with this transverse channels 211 of the Diameter after smaller piston stage 212, which in the frustoconical Sealing body 202 runs out with the the two valve bodies 187 and 203 bordered inner annular space 213 of the lowering valve unit 14 '' in constantly communicating Connection is established.

At one the inner opening of the longitudinal channel 209 coaxially surrounding annular shoulder 214 of the stepped piston 203, on the one hand, and the screw plug opposite this 184, on the other hand, is under moderate bias standing valve spring 216 supported the sealing body 202 of the inner valve body 203 in contact with its valve seat 201 and thus also the outer, cup-shaped Valve body 187 in contact with the valve seat fixed to the housing 191 is pushing. This "closed" configuration of the lowering valve unit 14 '' of the stroke control valve 14 is both the basic position shown in the circuit diagram of FIG. 1 0 of the stroke control valve 14 as well as that in the Longitudinal sectional view of FIG. 2 functional position I assigned to the stroke control valve 14 with which the Load-lifting operation of the stroke drive cylinder 11 knotted is.

The - annular space - consumer connection chamber 118 is via a fixed throttle 217 with the outer pressure chamber 183 in constantly communicating connection, so that in the in the 2 and 2a shown, locking configuration of the Lowering valve unit 14 ″ in the outer pressure chamber 183 the same pressure as in the B-consumer connection chamber 118. A functional of the throttle 217, which in the 2 and 2a as a stepped bore parallel to the central Longitudinal axis 111 of the stroke control valve 14 extending central Axis 218 is shown, corresponding throttle could also, as indicated by dashed lines, by a narrow longitudinal groove 217 'shallow radial depth of the outer Valve body 187 of the lowering valve unit 14 '' or a corresponding longitudinal groove 217 ″ of the central bore 186 the intermediate wall 182 of the lowering valve unit 14 ″ receiving housing part 117 can be realized.

The housing part 117 containing the lowering valve unit 14 ″, which must be prefabricated as a separate part from the control block 110 in the exemplary embodiment of the hydraulic installation 10 selected for explanation, can be described in detail in the structure of the control block 110 The layering technique explained can be composed of segment sheets 1171 to 11710, if necessary, of different thicknesses, for which a possible division is indicated by dashed-line solder joints 220 (FIG. 2a), with the selection of which only minor and easy preprocessing of the segment sheets 117 ₄ , 177 ₅ and 117 ₆ are required before the segment sheet package 117 ₁ to 117 ₁₀ forming the housing part 117 can be soldered together.

This leads to a possible layer structure of the housing part 117 The same applies analogously to the tank connection chamber 121 fixed housing part 119, in which the Spindle drive 94 is arranged, which is the drive clutch of the stepper motor 96 with the valve piston 14 ', the housing part arranged in the area of the pressure compensator 79 139, in which the pressure relief valve 83 of the pressure supply unit 52 is integrated and also for that in the 2 further shown, laterally on the control block 110 attached housing part 219, some of which is the valve seat sleeve 174 of the tilt actuator 19 assigned Shuttle valve 68 is added.

The overall configuration of the arrangement shown in FIG. 2 of the motor-controlled main piston 14 ', the valve body 187 and 203 of the lowering valve unit 14 '' of Stroke control valve 14, the piston 84 of the pressure compensator 79, the Valve body 151 of the check valve 73, the valve ball 221 of the shuttle valve 14 associated with the stroke control valve 72 and the valve ball 222 of the tilt control valve 33 assigned shuttle valve 68 corresponds to a stationary Operating state of the hydraulic installation 10, in which the piston 13 of the stroke drive cylinder 11 with constant Speed in load-lifting mode moved upwards, while the other hydraulic drives 19, 26 and 28 have stopped, i.e. the control valves assigned to them 33, 34 and 36 in their blocking basic positions 0 are held.

The motor-driven is in the above-mentioned stationary operating state Main piston 14 'so far from its spring centered Middle position - away from the lowering valve unit 14 '' - disengaged that an annular groove 223 of the piston 14 ', the 128 between the central piston flange and its piston chamber-side piston flange 127 arranged is and in every possible position of the motor-driven Piston 14 'in communication with the pressure (P) supply line 49 Connection is established via the now released Throttle gap 152 also with the A consumer connection 63 is communicatively connected and pressure medium over this and the one opened against the action of its valve spring Check valve 73 in the drive pressure chamber 12 of the stroke drive cylinder 11 can flow.

The pending at A consumer connection 63, with good approximation corresponding to the operating pressure in the drive cylinder 11 Pressure is also on the load sensing port 57 of the Stroke control valve 14 and causes that associated with it Shuttle valve 72 comes into that functional position, in which the pending operating pressure also enters the operating pressure chamber 88 of the pressure compensator 79 is coupled. This pressure is due to that which occurs across the throttle gap 152 Pressure drop lower than the pressure below the that via the pressure (P) supply line 49 to the stroke control valve 14 inflowing pressure medium is available, which also in the Reference pressure chamber 89 of the pressure compensator 79 is coupled.

The flow path required in this regard, to which the reference pressure connection 81 corresponds in the circuit diagram in FIG. 1, is through a transverse channel 224 which is in constant communication with the pressure (P) pressure supply line 49 and also with this and with the reference pressure chamber 89 of the pressure compensator 79 formed in a continuously communicating longitudinal channel 226 of the pressure compensator piston 84. Due to the positive pressure difference Δp between the reference pressure p _R coupled into the reference pressure chamber 89 in the stationary operating state and the operating pressure p _B coupled into the operating pressure chamber 88 of the pressure compensator 79, the pressure compensator piston 84 has an equilibrium position deflected against the restoring force of the balance spring 93 compared to its basic position, in which a throttle gap 229 is released between a piston-side control edge 227 and a housing-side control edge 228 of the control block 110, via which pressure medium can flow back from the pressure (P) supply line 49 to the unpressurized tank space 54 ′ or to the reservoir 56 of the pressure supply unit 52.

The pressure p _B prevailing in the drive pressure chamber 12 of the stroke drive cylinder 11 is also coupled into the B consumer connection chamber and prevails - in the stationary operating state - also in the outer pressure chamber 183 of the lowering valve unit 14 '', the valve bodies 187 and 203 of which are thereby additionally Force against their associated valve seats 191 and 201 are pushed.

To stop the stroke drive 11, the main piston 14 'of the stroke control valve 14, controlled by the stepping motor 96, is set to the basic position 0, in which, due to the position of the main piston 14', the pressure (P) supply line 49 is shut off from the a consumer terminal 63, this, however, 128 of the main piston and that arranged adjacent the edge 126 _'12 due to a shared in this basic position gap between the central flange at the central longitudinal axis 111 of the lift control valve 14 coaxial recess 126 _{12 of} the segment plate 122 _{12 of} the control block 110 released annular gap communicates with the unpressurized return (T) connection 48.

The consequence of this is that the check valve 73 in its Locked position and because the lowering control valve unit 14 '' is in its locked position the lift stops with the load supported on it.

If the pump drive 92 is not switched off the piston 84 of the pressure compensator 79 passes through the Effect of the coupled in their reference pressure chamber 89 Output pressure of the pump 91 in a control position in which in the housing channel 137 of the control block 110 between the Pressure (P) supply line 49 and the tank space 54 ' Throttle gap 229 is released, in a recirculating mode the pump 91 pressure medium from the pressure (P) supply line 49 "direct" to the return line 54, i.e. to the Reservoir 56 of the pressure supply unit 52 flows back.

Also the starting position 0 of the main piston 14 ' the stroke control valve 14 is expediently motor-controlled, controlled by the electronic control unit 103 to ensure that the lifting platform gently runs in to ensure the standstill and unwanted vibrations or to avoid vibrations. The necessary for this Load information is characteristic of the pressure Output signal of the pressure sensor 107 provided.

As soon as the basic position 0 of the main piston 14 ′ of the stroke control valve 14 is reached, which the electronic control unit 103 recognizes from the relevant output signal of the reference signal generator 102, the electrical control of the stepping motor 96 can be canceled, since the main piston 14 ′ is caused by the action of the return springs 17 and 18 is held in the basic position 0. In the basic position 0 of the main piston 14 ', support rings 231 and 232, via which the return springs 17 and 18 of the stroke control valve 14 act on the end faces 233 and 234 of the respective piston end flange 129 and 127 which face away from one another, are against stop surfaces 233' fixed to the housing. or 234 ', with which, in the basic position 0 of the main piston 14', its end faces 233 and 234 are aligned. The stop surface 233 'for the support ring 233 of the motor-side valve spring 17 is formed by a radial inner shoulder of the housing part 119, which forms the housing-fixed boundary of the tank connection chamber 121, within which the spindle drive 94 for driving coupling of the stepping motor 96 to the main piston 14' is arranged ; the stop surface 234 ', on which - in the basic position 0 of the main piston 14' - that support ring 232 is supported, on which the other valve spring 18, which is arranged in the tank space 54 ', acts on the inner ring rib 189 of the lowering valve unit 14'' Housing part 117 is supported, is formed by the edge of the tank chamber side of the circular opening 1268 coaxial with the central longitudinal axis 111 of the stroke control valve 14 of the segment plate 122 ₈ which delimits the tank chamber 54 'from the pressure (P) supply line 49.

The main piston 14 'of the stroke control valve 14 has on its side facing the lowering valve unit 14''a cylindrical extension 236 which passes through the support ring 232 arranged in the tank space 54' and whose diameter is slightly smaller than the inside diameter of the support ring 232. This extension tapers over a truncated cone-shaped chamfer 237 to a cylindrical actuating section 238, the diameter d _{3 of which is} slightly larger than the diameter d _{1 of} the central opening 198 of the bottom 194 of the cylindrical cup-shaped valve body 187 of the lowering valve unit 14 ″. This cylindrical actuation section 238 is followed by a slender, tappet-shaped end section 239, the diameter d ₄ (FIG. 2b) of which is significantly smaller than the diameter d1 of the central bottom opening 198 of the cup-shaped valve body 187.

In the basic position of the main piston 14 ' whose tappet-shaped end section 239 in the in FIG. 2a dashed position in which its end face 241 either on the opposite end face 242 of the frustoconical sealing body 202 of the lowering valve unit inner valve body 203 14 '' "already" or a small distance from this is arranged so that only a few control pulses, through which the stepper motor 96 in the sense of a displacement of the piston 14 'towards the lowering valve unit 14 '' can be controlled, suffice to the plunger-shaped End portion 239 in contact with inner valve body 203 to bring and this with further control of the stepper motor in the same direction from that on the other valve body 187 arranged valve seat 201 so that the in Fig. 2b qualitatively shown configuration of the Pistons 187 and 203 of the lowering valve unit 14 '' reached is opened in the inner seat valve 201, 203 is while the outer seat valve 187, 191 is still closed is.

Pressure medium in the drive pressure chamber 12 of the stroke drive cylinder 11 under one supported by the piston 13 Load and by which the drive pressure chamber 12 is movable limiting piston area is certain pressure now via the B consumer connection 64, the B consumer connection chamber 118, the fixed throttle 217, the outer pressure chamber 183 of the housing part 117, the interior 207, the Longitudinal channel 209 and the transverse channels 211 in the inner annulus 213 of the piston arrangement 187, 203 and over the now released valve gap 242 (Fig. 2b) in the unpressurized Tank space 54 'of the stroke control valve 14 and via this to Outflow the reservoir 56 of the pressure supply unit 52, with the result that the lift of the forklift is lowered becomes. Provided that the free cross-sectional area of the valve gap 242 is significantly smaller than the free flow cross section of the throttle 217, is the Sinking speed essentially due to the throttling effect of the inner seat valve 201, 203 at the given Load determined and by motor-controlled adjustment the valve gap width can be selected. On the other hand, is the throttling effect of valve gap 242 is significantly smaller than that of the fixed throttle 217 is at a given load the lowering speed by the fixed throttle 217 determined and limited to a load-dependent maximum value.

The type of lowering operation explained so far sensitive adjustment of the throttle effect of the inner valve body 203 and its seat 201 on the outer Valve body 187 formed "pre-relief" valve and Limitation of the maximum sink rate by the Fixed throttle 217 is useful when the one to be lowered Load large and accordingly the pressure is high under which the pressure medium in the drive pressure chamber 12 of the stroke drive cylinder 11 and in directly communicating with it Connected B-consumer connection chamber 118 the lowering valve unit 14 ''.

On the other hand, the load to be lowered is comparatively low and consequently also the pressure under which the hydraulic medium in the drive pressure chamber 12 of the stroke drive cylinder 11 stands, with the possible consequence that the only by Opening of the pre-relief valve 201, 203 achievable lowering speed would be undesirably low, the effective outflow cross-section of the lowering valve unit 14 '' can be enlarged by further deflection of the main piston 14 'also the further, through the cup-shaped Valve body 187 and the associated Valve seat 191 formed valve of the lowering valve unit 14 '' is opened and thereby the qualitatively in 2c shows the configuration of the valve body 187 and 203 is reached in the print medium from both the by the two valve bodies 187 and 203 bordered annulus 213 as well as the outer one, by lifting the Pot-shaped valve body 187 from the valve seat 191 released valve gap 243 directly from the B consumer connection chamber 118 flow into the unpressurized tank space 54 ' can.

The cylindrical actuating section 238 of the piston extension 236 is on its level with the tank side Boundary surface 196 of the valve body bottom 194 in Provide notches 244 on the end face reaching the system, then also via the pressure medium from the annular space 213 can flow out sufficiently freely if the cylindrical Actuating section 238 at which the central floor opening 198 surrounding edge area is supported.

Claims (14)

1. Hydraulic installation for a forklift truck, having a hydraulic lift drive for a lifting platform and at least one further hydraulic drive, particularly a hydraulic tilt positioning drive, and, individually assigned to these hydraulic drives, electrically driveable valve arrangements by means of which the operating pressures and pressure-medium flow rates required for the different movements of the lifting platform can be controlled, the lift drive being designed as a single-acting hydraulic cylinder whose lifting and lowering operations are controllable through valve-controlled inflow of pressure medium to the drive pressure space and valve-controlled outflow of pressure medium from this drive pressure space of the hydraulic cylinder respectively, and there being provided for this purpose a lift control valve arrangement which is controllable out of an initial position (0), in which the drive pressure space of the lift drive cylinder is blocked against both the pressure output of the pressure supply unit and against its return (T) connection, into a functional position (I), assigned to the lifting operation, in which the drive pressure space of the lift drive cylinder is connected to the pressure (P) supply output of the pressure supply unit but blocked against its return (T) connection, or, alternatively, is controllable into a functional position (II) assigned to the lowering operation of the lift drive cylinder, in which the drive pressure space of the lift drive cylinder is connected, via flow path of the valve which is released in this position, to the return (T) connection of the pressure supply unit but blocked against its pressure (P) output, the amounts of the flow-path cross-sections released in the functional positions I and II being controllably settable and increasing amounts of the flow cross-sections of the flow paths released in the respective functional position (1 or II) corresponding to increasing amounts of the displacements of a piston of the lift control valve arrangement out of its middle position,
   characterized by the following features:

   a) the lift control valve arrangement is designed as a multiway/3-position valve (14) which has a main piston (14') which is movable, by means of an electric positioning motor (96), into its positions, corresponding to the different functional positions (0, I and II) of the lift control valve arrangement (14), which, due to positive motional coupling of the valve piston (14') to the drive shaft of the positioning motor (96), have a defined relationship to the, relative to a reference position, azimuthal positions of the rotor of the positioning motor;

   b) the positioning motor (96) is designed as a digitally driveable motor, the rotor of which, by forced operation, attains an azimuthal position of its drive shaft which is coded into a digital drive signal,

   c) a pressure sensor (107) is provided which generates electrical output signals which are characteristic of the pressure in the drive pressure space (12) of the lift drive cylinder (11) and are supplied to an electronic control unit (103) which, in dependence on the output signals of the pressure sensor (107) which are characteristic of the pressure and, consequently, the load, provides for an automatic limitation of the control stroke of the main piston (14') of the lift control valve (14) to an amount, to which there corresponds a maximum value of the lifting or lowering speed of the lifting platform that is permissible in relation to the load, below which a dynamically stable lifting and lowering operation of the lifting platform which is substantially free from rocking motion is assured.
2. Hydraulic installation according to Claim 1, characterized in that, a non-self-locking gearing is provided for the mechanical drive coupling of the positioning motor (96) and the main piston (14') of the lift control valve arrangement (14), and the initial position (0) of the main piston (14') is centred by means of restoring springs (17 and 18).
3. Hydraulic installation according to Claim 2, characterized in that the mechanical gearing is designed as a spindle-nut drive mechanism (94) in which the spindle (97) is preferably designed as a thread section of the drive shaft of the positioning motor (96) and the spindle nut (98) is fixedly joined to the piston (14') and is preferably made in a single piece with the piston which is movably guided in a torsionally rigid manner in the valve housing.
4. Hydraulic installation according to any one of Claims 1 to 3, characterized in that, upon a displacement of the valve main piston (14') out of its middle position for the purpose of a transition into the functional position (II) of the lift drive control arrangement (14) which is assigned to the lowering operation of the lift drive cylinder (11), a first seat valve (201, 203) first comes into its open position in which a pressure space (183) of the lift control valve arrangement (14) which communicates continuously, via a fixed throttle (217) with a B load connection chamber (118) which communicates continuously with the drive pressure space (12) of the drive hydraulic cylinder (11), comes into communication with the tank connection space (54') of the lift control valve (14) via the increasingly opening valve gap (242) of this valve seat, and upon further displacement of the main valve (14') for the purpose of an enlargement of the cross-section of the flow-off path (108) of the lift control valve arrangement (14), there additionally comes into its open position a second seat valve (187, 191) via whose valve gap (243) the B load connection chamber (118) and, with the latter, the drive pressure chamber (12) of the lift drive cylinder (11), comes into direct communication with the tank space (54') of the main control valve arrangement (14).
5. Hydraulic installation according to Claim 4, characterized in that the first seat valve (201, 203) is designed as a check valve which is integrated into the second seat valve (187, 191) and can be deblocked by the displacement travel of the main control piston (14').
6. Hydraulic installation according to Claim 5, characterized in that the second seat valve (187, 191) is designed as a check valve which can be deblocked by the displacement movement of the main valve (14') and which, from a minimum displacement of the piston through the stop action of the latter with the valve body (187) of the second valve seat (187, 191), comes into its open position in which, with increasing further displacement of the piston (14'), the opening cross-section of the valve gap (243) of the second seat valve (187, 191) increases further, but the opening cross-section of the valve gap (242) of the first seat valve (201, 203) remains constant.
7. Hydraulic installation according to any one of Claims 4 to 6, characterized in that the second seat valve (187, 191) is designed as a ball seat valve which has a valve body (187), in the form of a cup sleeve, which, with a valve body section (199) in the form of a cylinder surface, forms the housing for the, in turn, cup-sleeve-type valve body (203) of the first seat valve (201, 203) which likewise has a sealing body (202), in the form of a truncated cone, which is pressed, by means of a valve spring (216), against a valve seat (201), in the form of a circular line, on the base (194) of the valve body (187) of the second seat valve within which there is delimited, by a section, close to the seat, of the valve body (187) of the second valve seat (187, 191) and by a smaller-diameter piston step (212) of the valve body (203) of the first seat valve (201, 203), an annular space (213) which communicates continuously with the outer pressure space (183) of the lift control valve arrangement (14) via transverse channels (211) of the valve body (203) of the first seat valve (201, 203).
8. Hydraulic installation according to any one of Claims 1 to 7, the further hydraulic drive(s) being respectively realized by means of a double-acting hydraulic cylinder or by means of a push-pull operable hydraulic cylinder pair, which is/are controllable by means of a respective multiway/3-position electromagnetic valve whose control magnet system is designed as a double stroke system with two excitation windings through the alternative energizing of which positioning forces acting on the valve body in alternative directions can be exerted, the piston of the valve having a spring-centred middle position, corresponding to the initial position 0 of the valve, which corresponds to the stopped state of the respective drive, and alternative directions of the piston displacement being assigned to the alternative functional positions I and II which correspond to the alternative drive directions of the respective drive, characterized in that the valve (33, 34, 36) is designed as a pulse-width-modulated valve in which the excitation windings can be excited in continuous, rapid alternating sequence for different periods T1 and T2, so that the direction and amount of the displacement of the valve piston by which a defined flow cross-section or resistance is to be set for a selected functional position of the valve is determined by the ratio of the excitation times T₁ and T₂, the ratio T₁/T₂ = 1 being assigned to the initial position of the movable piston, and the sum T₁ + T₂ of the excitation periods for which the excitation windings (38 and 39) are periodically energized being made sufficiently small such that the displacement amplitudes of the movements of the valve piston produced in the effective equilibrium positions are significantly smaller than the maximum control stroke of the same, the sum of the drive times T₁ and T₂ corresponding to a predefinable constant value T, i.e., a modulation frequency f_m = 1/T, there being furthermore used, as excitation currents for the two excitation windings, direct currents whose pulse repetition frequency f_i is at least 10x and preferably 50 to 100x greater than the modulation frequency f_m, and the ratio T₁/T₂ is variable between 1/100 and 100/1.
9. Hydraulic installation according to Claim 8, characterized in that the frequency f_m with which the modulation pulses of the different periods T₁ and T₂ can be generated is at least 200 Hz and preferably between 400 Hz and 1000 Hz, and the pulse repetition frequency f_i is between 5 and 10 kHz.
10. Hydraulic installation according to any one of Claims 1 to 9, characterized in that the lift control valve (14) and the further lift control valve(s) (33, 34, 36) each have a load (x)-sensing connection (57) which, in the initial position (0) of the respective valve (14, 33, 34, 36), is connected to the return (T) connection (53) of the respective control valve (14, 33, 34, 36) and, in the alternative functional positions (I and II) of the respective control valve (14, 33, 34, 36), is connected either to the one load connection (63) or to the other load connection (64) of the respective control valve (14, 33, 34, 36), and these load (x)-sensing connections (57) are connected to supply connections (58, 61, 69, 71) of a respective shuttle valve (59, 68, 72) which form a pressure comparison arrangement via which the respectively highest sensed operating pressure is supplied to the load connection (78) of a pressure regulator (79) whose reference pressure connection (81) is connected to the pressure output (51) of the pressure supply unit (52).
11. Hydraulic installation according to any one of Claims 1 to 10, characterized in that a control block (110), forming the housing for at least the lift control valve (14) and preferably also for further control valves (33, 34, 36), has a multilayer structure of segment plates (122₁ to 122₁₄) which are hard-soldered to one another by their broad longitudinal delimiting faces and are provided with recesses through whose contour shape and arrangement in relation to one another the cross-sectional forms and the inside dimensions of transverse channels and longitudinal channels, as well as valve channels and control chambers within the control block (110) are predefined.
12. Hydraulic installation according to Claim 11, characterized in that an outer, "first" segment plate (122₁) and further segment plates (122₂ to 122₈) within the control block (110) are provided with circular openings (123₁ to 123₈) of equal diameter which, arranged in alignment with one another, form a transverse channel (132), serving as a pressure (P) supply connection, which opens into a longitudinal slot (124) of the inwardly following segment plate (122₉), the said longitudinal slot forming the pressure supply line (49) which leads to the pressure (P) supply connections (48) of the individual control valves (11, 13, 34, 36).
13. Hydraulic installation according to either of Claims 11 or 12, characterized in that the one outer, "first" segment plate (121₁) and further segment plates (122₂ to 122₅) disposed within the control block (110) are provided with circular openings (131₁ to 131₅) which, arranged in alignment with one another, form the return (T) connection channel (131) which opens into the return line (54), which in turn is bordered by slot-type recesses, to which the control valves (14, 33, 34 and 36) are connected.
14. Hydraulic installation according to any one of Claims 11 to 13, characterized in that the pressure (P) supply connection connector-piece (48') and/or the return (T) connection connector-piece (53') is/are soldered into an outer section of the P supply transverse channel (123) and of the return (T) return channel (131) respectively of the control block (110).

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