EP1178943A1

EP1178943A1 - Device for regulating the tilt function of a lifting mast, in particular for a fork-lift truck

Info

Publication number: EP1178943A1
Application number: EP00993835A
Authority: EP
Inventors: Wolfgang Koetter; Georg Winkes
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2000-02-19
Filing date: 2000-11-25
Publication date: 2002-02-13
Also published as: DE10007688A1; WO2001060734A1

Abstract

A device (10) for controlling the tilt function of a lifting mast (11), for a fork-lift truck (12) is disclosed, whereby a double-acting working cylinder (16), activating the lifting mast (11), is operated in a closed regulating circuit (55) on tilting. A setpoint generator (25) for the speed of tilt cooperates with control electronics (23), which obtain a measured value of tilt speed from a position sensor (27) and hence control an electromagnetically-operated distribution valve, such that any deviations are controlled out. The run-off control edge (42) in the distribution valve (21) is used for control of the volume flow with a driving load, such that complex pilot valves are not necessary.

Description

Device for controlling the tilting function of a mast, in particular for a forklift

State of the art

The invention relates to a device for controlling the tilting function of a lifting mast in a mobile work vehicle, in particular a forklift truck according to the type specified in the preamble of claim 1.

It is already such a facility for controlling the

Tilting function of a mast is known from DE 32 03 553 AI, in which a proportionally operating 4/3-way valve controls a double-acting working cylinder for the tilting function on a forklift. An electrofluidic tilting pressure sensor is connected to the working cylinder on the rod side, while a throttle check valve is connected to the associated hydraulic working line. If the fork is loaded in such a forklift, the weight of this load causes a moment around the pivot point of the mast in the vehicle. Depending on the position of the center of gravity, this leads to compressive or tensile force on the tilt cylinder. If the tilt function should now be operated in this direction, i.e. with a driving load, the tilt speed cannot be Current can be controlled, which is supplied on the other side of the cylinder. Rather, the volume flow running to the tank must be throttled so that the desired speed is obtained. With the present device with a throttle check valve in the working line, such a change in load direction when tilting the mast is difficult to master. Also, the signals of the tilt pressure sensor in connection with a stroke pressure sensor are only used to give the operator a warning signal for the tilting behavior of the forklift. The directional valve of the tilt function is operated by hand.

Furthermore, from DE 197 21 739 AI a hydraulic control arrangement for a forklift truck is known which, among other things, has a valve axis for the tilt function, in which a 6/3-way valve with electrical actuation controls a double-acting working cylinder. In order to make it possible to tilt when changing the load direction, there are between the working cylinder and directional control valve in each

Working line switched a so-called load holding valve, which work as hydraulically unlockable check valves. With this solution, the pressure on the cylinder inlet side controls the opening cross-section at the outlet control edge of the load holding valve. In this way, the speed of the working cylinder is regulated by the load holding valve. For example, the pressure on the inlet side increases when the speed of the working cylinder is less than the target speed, which is determined by the oil tightness. The load holding valve thus opens further and the speed increases. So there are changes in load direction in both

Direction of movement of the double-acting cylinder controllable when tilting; however, the disadvantage is Use of relatively complex, additional valves that have to be switched in both working lines.

Furthermore, it is also known to use so-called preload valves instead of such load-holding valves, which represent a combination of a pressure limiting valve and a check valve. Such biasing valves act like a pressure relief valve for the volume flow emerging from the working cylinder; this is set to a value that is higher than the highest load pressure that occurs. Such valves have the disadvantage that even for actuation in the load direction, a pressure must always be built up in the other cylinder chamber, which raises the pressure on the discharge side to the level of the pressure relief valve, which leads to energy losses in operation. The preload valves also require additional valve effort in both working lines.

Advantages of the invention

The device according to the invention for controlling the tilting function of a lifting mast in a mobile work vehicle with the characterizing features of the main claim has the advantage that it enables effective control of driving loads without additional valve elements between the working cylinder and directional control valve, so that the tilting function in both directions of movement even under load changes can be controlled safely and reliably. The device is therefore less expensive to build and, unlike hydromechanical concepts, has no tendency to vibrate. Furthermore, in the control electronics, a better application to the forklift can be carried out by means of appropriate software parameters by simplifying the controller tuning. Because the regulation of the incline speed too acts in operation without a driving load, there is therefore no need for a hydromechanical limitation of the incline speed by means of a current regulator or an individual pressure compensator. The position sensor in the device can also be used for further functions; its signals can be used to reduce the speed when approaching the stroke end in the manner of an electronic end position damping. It can also be achieved with the position sensor that a dependence of the maximum inclination speed on the inclination angle can be achieved.

The device according to the invention for controlling the tilt function uses the knowledge that the control edge on the slide of the directional control valve, which connects the working cylinder connection to the tank, can be used to regulate the speed of the working cylinder in the event of a driving load. Depending on the load state, whether driving or driven, this control edge must be opened to different degrees so that the desired volume flow can pass. In order to be able to set the desired speed regardless of the load condition, the cylinder drive is operated in a closed control loop. Via a position sensor, which detects the movement of the mast, depending on the design, path, angle or speed, the movement of the

Detect tilt cylinder. The electrical output signals of the position sensor are fed to control electronics, the controllers of which carry out a comparison with the setpoint and correct deviations. For this purpose, an electrically actuated directional control valve is required, the energization of the actuating magnets being used as manipulated variables for the controller.

The measures listed in the dependent claims are advantageous further developments and improvements in Main claim specified facility possible. An embodiment according to claim 2 is particularly advantageous since a speed control loop allows particularly simple control. Also favorable are versions according to claims 3 and 4, whereby no operation of the hydraulic pump is required when tilting with sufficient driving load pressure, since the required amount of oil is sucked in by the double-acting working cylinder. This not only leads to energy savings, but also has noise advantages. Furthermore, an embodiment according to claim 5 is particularly expedient, since it can be used to carry out an emergency shutdown and high requirements with regard to tightness can be met, so that a simpler and cheaper control valve can be used. An embodiment according to claim 7 also favors the control of the tilt function without operating the hydraulic pump. Further advantageous embodiments result from the remaining claims of the description and the drawing.

drawing

An exemplary embodiment of the invention is shown in the drawing and explained in more detail in the following description. FIG. 1 shows a device for controlling the tilting function of a lifting mast for a forklift in a simplified representation, and FIG. 2 shows the hydraulic block for the device according to FIG. 1 in a simplified representation.

Description of the exemplary embodiment

1 shows a simplified representation of a device 10 for controlling the tilting function of a lifting mast 11 in a mobile work vehicle, which is designed here as a forklift 12. The lifting mast 11 with its lifting device 13, which is of no interest here, is shown in FIG in a known manner with the help of an axis 14 pivotally mounted on the housing 15 of the forklift 12. A hydraulically actuated, double-acting working cylinder 16 is articulated on the housing 15 and on the mast 11; with it, the lifting mast 11 can be held in its respective position or tilted forwards in the direction of travel of the forklift 12 and backwards against the direction of travel. This working cylinder 16 is therefore also referred to as a tilt cylinder and is usually designed as a differential cylinder.

To actuate the working cylinder 16, a valve block 17 is provided, which is connected to a pump 18 for pressure medium supply and to a tank 19 m for relief. The valve block 17 itself has an electromagnetically controllable, proportionally operating 4/3-way valve 21, which is followed by an isolating valve 22. For the electrical control of the directional control valve 21, the device 10 has control electronics 23 which are supplied by an electrical energy source 24 with current or

Voltage is supplied. Furthermore, the control electronics 23 are operatively connected to an electromechanical setpoint generator 25, which is arranged in a fixed position in the forklift 12 and at whose input 26 setpoints for the desired tilting speed can be set.

Furthermore, an electromechanical position sensor 27 is arranged in the forklift 12, which detects the movement of the mast 11 when tilting and reports actual values dependent thereon as electrical signals to the control electronics 23. The actual and target values are controlled by the controllers of the

Control electronics 23 compared and, depending on this, generated manipulated variables for correcting the control deviation, the energizing of the actuating magnets 28, 29 on the directional control valve 21 serving as the manipulated variable. FIG. 2 now shows the valve block 17 according to FIG. 1 more closely with its connection, the individual valve elements being shown in simplified form in the form of circuit symbols. The valve block 17 is traversed by an inlet channel 31 connected to the pump 18 and by a return channel 32 connected to the tank 19, so that additional valve blocks for other functions of the forklift, for example for the lifting cylinder, can be attached. From the inlet channel 31, an inlet line 33 leads via a pressure compensator 34 to one labeled P

Inlet port 35 of the 4/3 way valve 21. A return port 36, denoted by R, is connected to the return channel 32 via a return line 40. Working lines 39 and 41 lead from the two motor connections 37 and 38 of the directional control valve to connections A and B. In these working lines 39, 41, the isolating valve 22 is connected, which in a spring-centered basic position 42 with its seat valves 50 connects A and B securely seals. The release valve 22 is by a magnet 43 in one

Open position 44 adjustable. This release valve can also advantageously be designed as a pilot-operated valve.

On the directional control valve 21, the magnets 28, 29 are combined to form a double stroke magnet and from it the associated slide can be deflected into a first working position 45, in which the inlet connection 35 is connected to the second motor connection 38 via an inlet control edge 46 functioning as a metering orifice, while the first

Motor connection 37 is connected to the return connection 36 via a flow control edge 47. The directional control valve 21 additionally has a control connection 48, via which in the first working position 45 the load pressure downstream of the measuring orifice 46 and thus in the second motor connection 38 tapped and led to the pressure compensator 34 via a control line 49. Furthermore, this control connection 48 is connected to the return line 40 via a suction valve 51, the suction valve 51 opening towards the control connection 48. The control line 49 is also connected to a control line system 52 which is not of interest here. The directional control valve 21 also has, in addition to its central position 53, a second working position 54 in which the connections are now interchanged so that the drain control edge 47 is now connected between the second motor connection 38 and the return connection 36, while the measuring orifice 46 is between the inlet connection 35 and the motor connection 37 lies. The directional control valve 21, which is designed as a proportionally operating control valve, is also expediently designed such that its drain control edge 47 in both

Working positions 45, 54 advanced over the inlet control edge 46.

The control electronics 23, the valve block 17, the tilt cylinder 16 and the two transmitters 25 and 27 form parts of a control circuit 55, in which the tilt speed is primarily used as a control variable.

The operation of the device 10 is explained as follows, reference being made to FIGS. 1 and 2. The release valve 22 is only required in connection with the inclination control if the requirements for tightness with the slide seal in the directional control valve 21 cannot be represented. The release valve 22, which is equipped with tight seat valves 50, is electrically actuated and is switched into its open through position 44 before the control slide in the directional control valve 21 is actuated. For the explanation of the function of the tilt control, it should now be assumed that pressure medium from the directional control valve 21 via the port B m controls the piston chamber of the working cylinder 16 in order to tilt the lifting mast 11 m forward in the direction of travel. It is assumed that there are driving load conditions, the connection A and thus the first motor connection 37 being loaded by the engine pressure. When the control slide in the directional control valve 21 is deflected from the middle position 53 m of its first working position 45, the drain control edge 47 is opened by the advance of the drain control edge 47 with increasing slide travel, after which the feed control edge 46 working as a measuring orifice can only open. The load pressure in the tilt cylinder 16 leads to a flow as soon as the drain control edge 47 m of the first working position 45 opens. The tilt cylinder 16 moves, a negative pressure being generated at the second connection 38 and thus at B, since the inlet control edge 46 has not yet released the connection between the inlet connection 35 and the second motor connection 38. This also applies to

Operating points at which the orifice 46 is open, but due to the driving load conditions, the outflowing volume flow in port A exceeds the inflowing amount to port B. The area ratio of the normally available differential cylinder also requires a higher current in B than the amount flowing out of A. In these cases, the suction valve 51 now takes effect by allowing pressure medium to flow in from the return line 40 via the suction valve 51, the control connection 48 and the second motor connection 38 to the connection B. Through the control electronics 23 operating as a controller, the sequence control edge 47 is opened as far as is necessary for the realization of the desired incline speed. The control electronics 23 and the directional control valve 21 work as Parts of a closed control loop, in which the desired incline speed is specified by the setpoint generator 25, while the position sensor 27 determines the actual value of the incline speed and reports it to the control electronics 23. The electronic control unit 23 carries out the comparison between the setpoint value and the actual value and regulates any deviations that occur, the energization of the magnets 28 and 29 serving as the manipulated variable of the controller.

If the driving load pressure is not sufficient in this process to achieve the desired incline speed or even the load pressure m acts in the opposite direction, the controller m of the control electronics 23 will further increase the control of the control slide in the directional control valve 21. As a result, the orifice 46 is opened until the desired oil flow flows to the second motor connection 38 and thus to the connection B. The difference between an operation with a driving load and an operation with a driven load therefore lies in a differently large deflection of the control slide in the directional control valve 21 and thus in a differently wide opening of the control edges 47 and 46. With the directional control valve 21, which is designed as a proportional control valve is, the speed when tilting the

Lift mast 11 can be regulated forward in the direction of travel, which is possible both with driven and with driving load conditions. By regulating the incline speed for the case of the driving load with the aid of the sequence control edge in the directional control valve 21, complex load holding valves or preload valves can be saved in the working lines. This in particular reduces the number of hydraulic control elements, so that the vibration behavior of the device 10 is considerably improved. The tilt control can take effect in a corresponding manner if the directional control valve 21 is controlled into its second working position 54 in order to tilt the lifting mast 11 backwards against the direction of travel. Here, too, the leading sequence control edge 47 can have the same effect.

The pressure compensator 34 is designed as an individual pressure compensator for the directional control valve 21 and is intended to ensure a control pressure gradient on the measuring orifice and thus the inlet control edge 46 which is independent of the load pressure. Under certain circumstances, this pressure compensator 34 can be omitted if the accuracy requirements for the control are not very high under favorable operating conditions. If, in an embodiment with a pressure compensator 34 missing, the pressure difference increases, for example in the case of parallel actuation, the device 10 for tilt control can counteract by reducing the deflection of the directional control valve 21 accordingly and thus keep the tilt speed constant.

Of course, changes are possible to the illustrated embodiment without departing from the spirit of the invention. Thus, the release valve 22 can also be omitted if sufficient tightness is ensured by the directional valve 21 itself. The individual pressure compensator 34 can also be omitted if the requirements for the control quality are set low. The position sensor 27 can easily be designed so that it can work as a displacement, angle or speed sensor. Although the control loop can work particularly advantageously with a control variable tilting speed, the closed control loop can also be designed and operated as a position control loop. Directly controlled valves as well as pilot operated valves are suitable as control directional valves. You can also set the travel setpoint of a subordinate slide position controller as a manipulated variable for the controller.

Claims

Expectations

1.Device for controlling the tilting function of a lifting mast in a mobile work vehicle, in particular forklift truck, with a double-acting hydraulic working cylinder serving to tilt the lifting mast, which can be controlled by a proportional directional control valve which is connected to a hydraulic system with a pressure medium source and with one The sensor assigned to the working cylinder, the electrical signals of which can be fed to an electronic unit, characterized in that the sensor is a position sensor (27) which detects the movement of the lifting mast (11) when tilting, the electrical signals of which can be fed to control electronics (23) which are connected to a Setpoint generator (25) for the tilt function is connected and that the directional valve (21) can be actuated electromagnetically and can be controlled by the control electronics (23) to form a closed control loop (55).

2. Device according to claim 1, characterized in that the working cylinder (16) is operated in a closed speed control loop (55) in which the setpoint generator (25) specifies a measure of the incline speed.

3. Device according to claim 1 or 2, characterized in that the directional control valve (21) has at least one working position (45, 54) in which the motor connection (38, 37) located downstream of the inlet control edge (46) via a suction valve (51 ) is connected to a return side (32, 40).

4. Device according to claim 3, characterized in that the directional control valve (21) has a control connection (48) which is associated with a load pressure tap in working positions (45, 54) and which is connected via the suction valve (51) to the return side (32, 40 ) Connection, the suction valve (51) is designed to open towards the working cylinder (16).

5. Device according to one of claims 1 to 4, characterized in that between the directional control valve (21) and working cylinder (16), an isolating valve (22) is connected, which has the working cylinder (16) tight shut-off seat valves (50).

6. Device according to one of claims 1 to 5, characterized in that the directional control valve (21) in the feed line

(33) is preceded by a pressure compensator (34) which keeps the pressure drop at the measuring throttle (46) of the directional control valve (21) constant.

7. Device according to one of claims 1 to 6, characterized in that in the working position (45, 54) of the directional control valve (21), the drain control edge (47) with respect to the inlet control edge (46) working as a measuring throttle is designed to be leading.

8. Device according to claim 3 or 7, characterized in that the directional valve (21) on both sides a middle position (53) each has a working position (45, 54).

9. Device according to one of claims 1 to 8, characterized in that with the help of the double-acting working cylinder (16) of the lifting mast (11) can be inclined in both directions from a particularly vertical central position.