Abstract:
The procedure, provides a simple and retro-fittable manner to align working equipment, mounted to a liftable and lowerable hoisting frame of a working machine in a tilting way to comply with required positions, wherein the working equipment is shifted via a tilting cylinder in other directions than the hoisting framing. The tilting cylinder is supplied with hydraulic oil from a hydraulic pump for the working hydraulic system by a direct-operated control valve, and secondary consumers of the working machine being supplied with hydraulic oil from at least one other hydraulic pump. Once the driver operates a triggering element, the two hydraulic connections of the tilting cylinder are also connected to the hydraulic pump for the secondary consumers by a switch-over valve activated by the control equipment, therefore shifting the tilting cylinder in the direction of the neutral position of the working equipment.

Description:
This application is the US National Stage filing of International Application Serial No. PCT/EP2007/003722 filed on Apr. 27, 2007 which claims priority to German Application DE 10 2006 024 731.0 filed May 26, 2006. 
     Mobile working machines, including wheeled loaders/tractor shovels, will have working equipments which are mounted on the frame of the working machine by means of a liftable and lowerable hoisting framing. For prompt working sequences, it is reasonable (especially when working with a tractor shovel) to return the hoisting framing, once it has been emptied in the lifted position of the hoisting framing and lowered down again, automatically to a position with ground contact which allows the driver to continue his work, i.e. picking up new material with the shovel base, without having to modify the position, the shovel base being set at a favourable angular position, approximately in parallel to the ground for example. Depending on the circumstances, it may be an advantage to be able to preset the shovel base in the direction of a certain positive or negative adjusting angle. In general, tractor shovels from a certain size, an operating weight of 7 tons for instance, today are provided with a hydraulic pre-control system for the control valve which provides for the operation of the hoisting and shovel tilting systems and in some cases additional functionalities. Such tractor shovels equipped with a pre-control system for the control valve are known to be equipped with automatic return control systems which shift the shovel back to a neutral position once it was activated (i.e. into the position in which it contacts the earth at a desired angle.) It is therefore necessary to intervene into the pre-control system for the hydraulic circuit triggering the shovel tilting function in order to activate the return system in the intended way. An intervention into the pre-control system will also have the benefit of only having to control a small oil volume at low pressures. 
     Such low oil deliveries also offer the advantage of low switching times of the solenoid valves which are therefore provided with low nominal diameters. The valve piston, however, will need a certain floating time in order to be shifted, by spring force, to its central position after reaching the corresponding angular shovel position. As the hydraulic pump will apply force for the working hydraulic system to the tilting cylinder(s) during this switch-off period, and as its rate of delivery depends on the drive motor speed prevailing during this period, the result will be a different overrun period of the tilting cylinder once the switch-off signal is activated so that the shovel does not contact the ground at a parallel position (or at a preset desired angle of adjustment). Either the disadvantageous shovel position affecting the next material loading sequence can be tolerated, or a shovel position largely independent from the motor speed by initiating other measures can be reached, as it is described in DE 44 37 300 C2, for instance. 
     The automatic return systems described above are therefore not only suitable for working machinery provided with hydraulic pre-control systems for the control valve. But tractor shovels of lower weight categories up to approximately 6 tons will frequently be direct-controlled, i.e. the driver-operated control lever directly acts on the control valve piston using a reversing gear. These working machines have no hydraulic pre-control system for the control valve which would allow for an implementation of the automatic return systems we know today. Kinematic systems for the hoisting and tilting mechanisms of working machines, especially tractor shovels of this type, are therefore mainly designed in such a way that the shovel is fully tilted out in its topmost hoisting framing position, and will contact the ground in an approximately parallel position when the hoisting mechanism lowers it down. This however only applies when lowering starts from the topmost position of the hoisting framing. If the shovel, in fully tilted position, is lowered from another, lower hoisting height, there will be strong deviation from parallelism. 
     A serious disadvantage will arise from the use of a stacker fork when the kinematic system is designed in this way. The fact that the tilting angle which places the shovel in a favourable position for material pickup from its ground position becomes larger, at least in the first part of the hoisting course, will result in the angular position of the fork taking the same course so that the driver will have to continuously readjust during lifting to keep the fork arms at an approximately parallel position to the ground. Dangerous circumstances will arise however when stacked material (a loaded pallet) is unloaded and lowered from a medium hoisting height, for instance, as it is the case when lorries or railway wagons are unloaded, and the fork arms are in a position parallel to the ground. If the driver is not careful to counter-control the movement, the arms will increasingly lower down to the front risking the loaded material to glide off the arms. 
     Tractor shovels of this weight category are increasingly used for stacking tasks so that kinematic systems are currently designed so that the stacker fork is guided in parallel during the entire hoisting course. If you now lower the hoisting framing when the shovel is fully tilted, the shovel will contact the ground at a strongly inclined angle, with its shovel blade or its teeth first. This shows the need for an automatic return system for working machinery with direct-operated control valve, too. 
     When using direct-operated control valves, the tilting piston of the titling mechanism can not be used to return the shovel as it would have to move independently of the control lever the driver is holding in his hand. This would only be possible with an expensive separation of the control gear from the control valve, fitting an actuating cylinder or any such device in between. The space needed alone would largely eliminate such an option, as the reversing gear is often directly mounted on the control valve housing. The oil volume required for an automatic return system would have to be received directly between the working hydraulic pump and the control valve, resulting in the requirement of a large nominal diameter of the valve, on the one hand, and the impossibility of the driver controlling the lifting function during automatic tilting back, on the other hand. In this case, once the tilting-back sequence has automatically stopped, the pump delivery would suddenly act on the lowering side of the hoisting cylinders so that the driver would no longer see at what moment the lowering behaviour would change. Such an approach is therefore impossible. 
     It would be desirable to provide an automatic return system for the tiltable working equipment of a working machine with a direct-operated control valve for the tilting cylinders, which is as simple as possible and which can be fitted at later times, for instance. 
     The driver operates a triggering element, two hydraulic connections of the tilting cylinder are also getting connected to the hydraulic-pump for the secondary consumers, therefore shifting the tilting cylinder in the direction of the neutral position of the working equipment, by means of a switch-over valve activated by the control equipment. 
     The delivery of the pump can be used for the secondary consumers for the automatic return system, and not for the use of the delivery of the pump for the working hydraulic system. The feed can either be received ahead of the hydromotor for the oil cooler fan, the fan running in the usually available free-wheel drive mechanism during the short period of back-tilting and only being subjected to low speed reduction, or it can be received after the fan, the force needed for shovel back-tilting being applied to the fan motor at its output orifice, the fan motor being enabled to absorb that force however. 
     The oil is fed to the tilting cylinder by an electromagnetic switch-over valve which is inserted in the supply line from the hydraulic pump for the secondary consumer. This switch-over valve has a switching diagram which, once the automatic return system is activated via the trigger element (switch), guides the oil delivery to the two tilting cylinder connections so that pressure is applied to the tilting cylinder according to the principle of a differential cylinder, which means that the piston rod extension speed depends on the volume released by it and which the pump delivery has to top up. 
     With the usual piston rod/cylinder area ratio of approx. 1:4, corresponding to a cylinder diameter which is about half the piston rod diameter, the piston rod will, in the case of a specified rate of delivery, be extended four times as fast as in the case of the cylinder only being pressurized on the piston side. As the rate of delivery of the hydraulic pump used for this purpose is only about half the rate of delivery of the hydraulic pump for the working hydraulic system, the piston rod is therefore extended with about double the speed compared to the use of the pump for the working hydraulic system. This results in that, in case of hoisting framing positions lower than maximum height levels, the working equipment (shovel) contacts the ground in an end position parallel to the ground, even after the automatic return system was triggered. This is a great benefit especially for tractor shovels of said weight categories (up to approx. 6 tons) and speedy workflows, when material will frequently only be poured onto a great heap and the hoisting framing needs not be hoisted until its topmost position. 
     An arrangement provides for the detection of the tilting cylinder position and its monitoring by the switch-over valve control unit, as well as for the switching of the switch-over valve control unit into a position in which the two tilting cylinder hydraulic connections will be shut off from the hydraulic pump for the secondary consumers once the pre-set neutral position of the tilting cylinder is reached. This ensures the exact alignment of the working equipment in the pre-set neutral position. 
     The preferred switch-over valve will be a 4/2-way directional control valve. 
     By preference, this working machine has a tilting cylinder which is equipped with a tilting cylinder position detection device which is connected to the control unit. The tilting cylinder is preferably designed or connected respectively as a differential cylinder. 
     In an arrangement, a nonreturn valve is provided in the hydraulic line between the switch-over valve and the tilting cylinder hydraulic connection on the piston rod side. This nonreturn valve ensures trouble-free function even though, with activated automatic return system, the driver may be operating, at the same time, the control valve in the direction of tilting. 
     The solution described above facilitates automatic shovel return systems of a simple structure with working machines, including tractor shovels with direct-operated control valves, which however still have advantages compared to conventional systems with control valves with hydraulic pre-control systems: 
     High adjusting speeds can be achieved due to the differential switchgear of the tilting cylinder so that low waiting times will occur once the automatic return system is triggered and the tractor shovel can drive back because the shovel is quickly tilted, when lorries are loaded, for instance, the front shovel area in tractor shovels of the said size categories engaging below the upper lorry dropgate edge. During shovel emptying, with a hoisting framing not lifted up to end position, such a high adjustment speed also enables the shovel to contact the ground in a parallel position when it is lowered. 
     The differential switchgear of the tilting cylinder along with its roughly fourfold speed increase is the reason why the pump for secondary consumers, having a lower delivery rate than that of the pump for the working hydraulic system, can be used in order to achieve an increase of adjusting speeds which will still be superior to all systems available today and meet all operational requirements. This will also enable you to keep all components of the system structure small due to the lower rate of delivery. 
     The desired end position of the working equipment (shovel) is controlled with high repeating accuracy, even with varying motor speeds resulting in different rates of delivery of the pump, as the switch-off process is triggered by a solenoid valve of a low nominal diameter. Said solenoid valves have switch-off times of less than 50 ms. In conventional systems, however, in which the control valve tilting mechanism piston is, via the pre-control system, responsible for deactivation of the return sequence, the shovel end position is strongly affected by the motor speed prevailing each time, as the actuating time of a solenoid valve, which you can find here as well, is increased by that of the tilting piston, which results in a multiplication of that of the solenoid valve. To compensate for this, additional devices will be necessary in all of the well-known systems. 
     The driver will not have to cope with any critical or unforeseeable operating situations, in cases where the automatic return system is triggered accidently, or if overloads occur. This also applies to the activation of the control valve tilting mechansim in any possible adjustment direction during the automatic return process. Additional fitting is easily made during final assembly of the machine, and retrofitting is easily possible after its delivery; all existing structural parts of the working machine remain unmodified. You only have to connect hydraulic lines of a low nominal diameter in addition to the simple electrical/electronic elements for signal transmission which can be easily mounted. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawing shows in 
         FIG. 1  shows a hydraulic circuit diagram for a tractor shovel not displayed in detail, 
         FIGS. 2 through 6  show the individual operating status of the hydraulic circuit diagram section affected as per  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A hoisting framing  1  of a tractor shovel, which is not is displayed in further details, is represented in a schematic form. This hoisting framing  1  can be lifted and lowered at a link point and is mounted to a tractor shovel frame whose details are not given here. At the lower end of hoisting framing  1 , there is some working equipment connected at a link point  3 , the working equipment forming a shovel  4  in this example of an arrangement. Said shovel  4  can be tilted, in relation to hoisting framing  1 , around link point  3  by means of an articulated lever mechanism  5 ,  6  using a tilting cylinder generally designated as  7 . 
     Tilting cylinder  7  has a piston rod  8  and a piston  9  and is mounted to the tractor shovel frame in an equally articulated way, through a link point  10  at the end opposed to piston rod  8 . 
     A carrying rod  11  is fixed to the end section of piston rod  8 , which is located outside the tilting cylinder, and this carrying rod  11  has at its free end a control flag  12 , which is part of a tilting cylinder position detection device. The tilting cylinder  7  proper is equipped with the second element of the tilting cylinder position detection device, which is in our example a component part designed as limit switch  13 , which is actively connected via an electrical signal line  14  with an electronic control unit  15  whose function is explained in the following. It is of course possible to design the tilting cylinder position detection device in another way. The only important thing is that it can detect the position of tilting cylinder  8  which corresponds to the specified neutral position of shovel  4  in relation to the ground  16  (shown in  FIG. 1 ). 
     The working machine, in the present example, the tractor shovel, has a drive engine, e.g. a Diesel engine  17 , driving three hydraulic units, namely a preferably adjustable hydrostatic travel drive  18 , a hydraulic pump  19  for the working hydraulic system of the tractor shovel, and at least another hydraulic pump  20  for secondary consumers. Hydraulic fluid is supplied from, or returned respectively to, a tank generally designated with  21 , by way of hydraulic units  18 ,  19 ,  20 . 
     Among other things, hydraulic pump  19 , of the working hydraulic system, is responsible for the driver&#39;s regular operation of shovel  4  via tilting cylinder  7 . Pump  19  is therefore, via a hydraulic line  22 , connected to a control valve  23  which the driver can directly operate using control levers  24 . Control valve  23  is connected to the piston side  26  via a hydraulic line  25 , and to the annulus collector  28  of the tilting cylinder  7  with a hydraulic line  27 . 
     Hydraulic pump  20  for secondary consumers is, for example, used to supply or drive a fan motor  30  driving a fan  31 . Hydraulic pump  20  is connected for this purpose to fan motor  30  via two hydraulic lines  32  and  33 , an electromagnetic 4/2 directional valve  34  being arranged between the two hydraulic lines  32  and  33 . In the home position of valve  34  shown in  FIG. 2 , fan motor  30  is connected to hydraulic pump  20 . A pressure-relief valve  42  safeguards hydraulic pump  20 . 
     Solenoid valve  34  moreover has two connections  35 ,  36 , a hydraulic line  37  being connected to annulus collector  28  of tilting cylinder  7 , the hydraulic line  37  being in turn connected to connection  35 , and a non-return valve  38  being inserted in hydraulic line  37 . A hydraulic line  39 , which in turn has a connection to the piston side  26  of tilting cylinder  7 , is connected to connection  36 . 
     The electromagnetic 4/2 directional valve  34  is connected to the control unit  15  via an electrical signal line  40 , and this signal line is in turn connected to a trigger element  41  designed as a switch. 
     If the driver wishes to trigger the automatic return system, he operated the switch or trigger element  41 , and this results in the control equipment  15  adjusting the 4/2 directional valve  34  into the switching position shown in  FIGS. 1 and 3  in which both the oil delivery of hydraulic pump  20  and the oil volume displaced out of the annulus collector  28  of tilting cylinder  7  which is now being added through connection  35 , will join to be supplied to the piston side  26  of tilting cylinder  7  via connection  36 , in order to apply pressure to tilting cylinder  7  according to the principle of a differentiating cylinder, i.e. the extension speed of piston rod  8  is defined by the oil volume released and to be topped up by the delivery of hydraulic pump  20 . In this position of solenoid valve  34 , the fan motor  30  is decoupled from hydraulic pump  20 . 
     Piston rod  8  of tilting cylinder  7  is being extended via hydraulic pump  20 , thereby conducting shovel  4  in neutral position, until the tilting cylinder position detection device  12 ,  13  has detected that the specified, desired maximum extension position of piston rod  8  and therefore the desired neutral position of shovel  4  is reached. A corresponding signal is transmitted via signal line  14  to control unit  15 , and this signal switches 4/2 directional control valve  34  into the home position shown in  FIG. 2  excluding any further oil supply from hydraulic pump  20  to tilting cylinder  7 .  FIGS. 2 through 6  show the individual operating status of the automatic return system. 
     In  FIG. 2  the automatic return system is not activated. Solenoid valve  34  switches on the oil supply from hydraulic pump  20  which can now freely flow to the secondary consumer(s) (fan motor  30 , for instance). The connections  35 ,  36  of tilting cylinder  7  are locked by action of solenoid valve  34  so that the driver&#39;s operation of control lever  23  (via control lever  24 ) which activates tilting cylinder  7  will not result in any mutual affection. 
     The position shown in  FIG. 3  is the condition after the driver activated the automatic return system with trigger element  41 . The delivery of hydraulic pump  20  joins with the oil displaced from the annulus collector  28  of tilting cylinder  7  to flow in the direction of the piston side  26  of tilting cylinder  7 . Both cylinder sides have the same pressure due to the connection made between them by solenoid valve  34 . The force applied to the outside by piston rod  8  equals the product of hydraulic pressure and piston rod area. The tilting mechanism of control valve  23  is not activated in this case, and the oil from hydraulic pump  19  for the working hydraulic system can continue to flow to tank  21  largely without being pressed. When the shovel reaches the parallel position which corresponds to the ground, which is detected by the tilting cylinder position detection device  12 ,  13 , the solenoid valve  34  switches off again, and the circuit diagram shown in  FIG. 2  is given. 
     In the representation of  FIG. 4 , the tilting cylinder  7  is additionally pressurized by the driver into the direction of “tilting” during the automatic return tilting process. Piston rod  8  continues to extend, but the differential effect of tilting cylinder  7  is nullified because the annulus collector  28  of tilting cylinder  7  is connected with tank  21  by means of control valve  23 . The non-return valve  38  inside hydraulic line  37  will prevent the deliveries from the two hydraulic pumps  19  and  20  flowing to annulus collector  28  of tilting cylinder  7 ; they can only flow, as desired, to the piston side  26 . The oil volume displaced from annulus collector  28  will be directly fed to tank  21 . After reaching the cylinder position corresponding to the ground parallelism, the solenoid valve  34  switches off, and there is again the diagram shown in  FIG. 2 , with the difference that shovel  4  continues to move in this direction if the driver keeps the tilting mechanism connected to “tilting” via the control lever. 
     In the situation displayed in  FIG. 5 , the tilting cylinder  7  is additionally pressurized by the driver in the direction of “Emptying” during automatic return tilting. Although such a procedure has no practical importance for the application of the tractor shovel, it may be noted here nevertheless that this then results in an emptying operation the driver apparently desired. Both oil deliveries are directed from the piston side  26  of tilting cylinder  7  into tank  21  by the opening of the return flow channel in control valve  23 , while the hydraulic pump  19  for the working hydraulic system is supplying oil to the annulus collector  28  which in turn is connected with the piston side  26  of tilting cylinder  7  both via the nonreturn valve  38  and solenoid valve  34 . Due to the dead weight of the working unit, the speed of the withdrawing piston rod  38  will be defined by the flow resistances inside the lines, the control valve  23  and the solenoid valve  34 . The shovel in any case will move into the direction of emptying controlled by the driver. 
     In the situation displayed in  FIG. 6 , a higher load F is applied to shovel  4  in the “Emptying” direction, exceeding the retention force due to the differentiation connection of tilting cylinder  7  after activation of the automatic return system. This may be the case if shovel  4  was only partially emptied because larger material quantities remain stuck or if, during work using a tree clamp or pipe clamp, the driver has accidentally operated switch  41  for the automatic return system while shovel  4  is still inclined to the front, still clamping the load. Tilting cylinder  7  will have the tendency to withdraw, but nonreturn valve  38  will prevent the pressure built up on the piston side  26  of tilting cylinder  7  from propagating into annulus collector  28 . A hydraulic force retaining tilting cylinder  7  may be generated, which equals the quantity of the product from piston area and the pressure of the pressure-relief valve  42 , so that the outside load can be retained in position. In this case, the hydraulic pump  20  for the secondary consumers will supply towards the tank via pressure-relief valve  42 . If the driver now operated the “tilting” function by means of control valve  23 , the annulus collector  28  of tilting cylinder  7  is released into the return channel in control valve  23 , and piston rod  8  will extend in the desired direction.