Patent Publication Number: US-7717664-B2

Title: Loader

Description:
FIELD OF THE INVENTION 
   The invention relates to a loader with a hydraulically actuated extension arm, a sensor for monitoring the load condition on the loader and a hydraulic arrangement for actuation of the extension arm and/or implement attached to the extension arm, the hydraulic arrangement exhibiting at least one hydraulic cylinder; at least one hydraulically actuated control device for controlling the at least one hydraulic cylinder, a hydro-mechanical actuating device for the generation of hydraulic control pressure signals for the at least one control device, a hydraulic source, a hydraulic tank and an electronic control unit. 
   BACKGROUND OF THE INVENTION 
   In the area of loaders, such as loading vehicles or telescopic loaders and the like, systems are previously disclosed which protect the vehicle from getting into an unsafe load condition. Unsafe load conditions arise, for example, when the vehicle overturns over the front axle as the result of a forward shift in the center of mass. In these systems, the hydraulic functions are braked and are brought to a halt as soon as a sensor detects that the vehicle is threatening to tip. Once the hydraulic actuators have been stopped, the only functions that can still be operated are those which bring the vehicle back into a safe condition, for example raising the extension arm, tilting back the implement or the load and retracting the extension arm. 
   In systems of this kind, it is sensible not to arrest the movements of an extension arm too abruptly, as this can lead to overturning of the vehicle due to the inertia of the load and the extension arm. It is sensible to slow down the functions progressively the closer the vehicle approaches to a critical operating condition or load condition. 
   WO 2004/007339 A1 discloses a system of this kind. Here a tipping moment acting on the vehicle is detected by a sensor and is transmitted to an electronic control unit. Also provided are a number of hydraulic cylinders for the lifting, lowering and telescoping of a telescopic extension arm as well as the electro-hydraulic actuation of the hydraulic cylinders. The system provides for the hydraulic functions for operating the hydraulic cylinders to be slowed down as a set threshold value for the tipping moment is approached, before the hydraulic cylinders come to a complete standstill. In this case, for example, the load signal is processed electronically and the possibilities for operation by the user are reduced and/or operation is prevented. The more advanced the technology, for example by the use of electronic control units, the easier is the intervention by means of the electronics. 
   For hydro-mechanical systems with mechanically controlled control devices, the characterizing features disclosed in WO 2004/007339 A1 do not find an application, because a hydraulically pilot-controlled system intervention is not possible in a controlled manner by such simple means in the functions, due to the absence of suitable electronics. 
   SUMMARY OF THE INVENTION 
   The underlying object of the invention is to propose a loader of the kind indicated by way of introduction, by which the aforementioned disadvantages are overcome. 
   According to the invention, a loader of the kind mentioned by way of introduction is configured in such a way that means for varying the control pressure are connected to at least one control pressure line running between the actuating device and the control device, by which means, depending on a sensor signal supplied by the sensor, the control pressure generated by the actuating device is capable of being varied. The operability of the hydraulically controlled control device is influenced via the means for varying the control pressure in such a way that the pressure in the control pressure line is reduced, so that the manipulating variable at the control device and thus the volumetric flow of hydraulic fluid for the hydraulic cylinder regulated via the control device is reduced. The control pressure in the control pressure line is reduced to an increasing extent in this way, the closer a critical value for the load condition is approached, which value is set by the electronic control unit. In order to prevent an operator from being able to bring the vehicle into an unsafe condition, which might ultimately result in the overturning of the vehicle, the functions of the hydraulic cylinder are initially slowed down in this way and are then finally brought completely to a halt. 
   The means for varying the control pressure preferably consists of at least one electro-hydraulic overpressure valve capable of being actuated by the electronic control unit. The electro-hydraulic overpressure valve can be opened progressively depending on the load signal supplied by the sensor and/or the overload signal. The closer one approaches to the pre-set threshold value, the greater is the threat of the vehicle overturning, and the less the overpressure valves are adjusted. On the basis of the resulting decreasing control pressure, the valve gate of the control device is deflected to a smaller extent, as a result of which the control devices send less volumetric flow to the hydraulic cylinder, which consequently comes to a halt increasingly slowly. The control device can be actuated as usual in the opposite direction of movement. It is naturally conceivable for a number of hydraulic cylinders to be arranged in the hydraulic arrangement, and thus for a number of control devices to be capable of being used for the control of the hydraulic cylinders by being hydraulically adjusted. In the event that a number of control devices and a number of hydraulic cylinders are used, a number of electro-hydraulic overpressure valves accordingly can be used, which are adjusted by the electronic control unit depending on the sensor signal. 
   In an alternate embodiment, the means for varying the control pressure comprises at least one electro-hydraulic pressure reduction valve capable of being actuated by the electronic control unit, which is arranged directly in a pressure control line for the valve gate of the control device. The electro-hydraulic pressure reduction valve can be actuated depending on the load signal supplied by the load sensor and/or the overload signal. The closer one approaches to the pre-set threshold value, the greater is the threat of the vehicle overturning, and the more the control pressure for the valve gate is throttled or reduced by the pressure reduction valve. On the basis of the resulting decreasing control pressure, the valve gate of the control device is deflected to a smaller extent, as a result of which the control devices send less volumetric flow to the hydraulic cylinder, which consequently comes to a halt increasingly slowly. The control device can be actuated in the opposite direction of movement from that which is customary. It is naturally also conceivable for a number of hydraulic cylinders to be arranged in the hydraulic arrangement, and thus for a number of control devices to be capable of being adjusted hydraulically for the control of the hydraulic cylinders. In the event that a number of control devices and a number of hydraulic cylinders are used, a number of electro-hydraulic pressure reduction valves can accordingly be used, which are adjusted by the electronic control unit depending on the sensor signal. 
   It is thus possible to restrict the movements of the extension arm in such a way that the vehicle is not able to get into a dangerous operating condition, in conjunction with which the operator, in addition to the warning signals which are generated anyway in the cab of the loader, will be made aware of the fact that, in spite of its adjustment default, the extension arm is moving increasingly slowly until it comes to a halt. 
   The hydro-mechanical actuating device is preferably configured as a joystick. Valves are actuated in this case by the corresponding mechanical deflection of a control lever, which valves are connected to the hydraulic source and the control pressure line and generate a control pressure for the control device of the hydraulic cylinder. 
   The loader is preferably configured as a telescopic loader, in conjunction with which the extension arm is capable of being varied via a first hydraulic cylinder in respect of its angle of attack and via a second hydraulic cylinder in respect of its length, in conjunction with which a third hydraulic cylinder may be provided, with which an implement arranged on the extension arm is capable of being caused to pivot. Thus, for example, the tilting back of a loading shovel filled with material can also lessen a critical load condition, but without the extension arm being moved. In any case, the overpressure valves or pressure reduction valves arranged in the control pressure lines of the control devices provide for a slow execution of the movements determined by the operating person, so that no disruptive inertia mass effects of the load material or of the extension arm occur, which can then provoke overturning of the loader in the vicinity of the threshold value range. 
   In another embodiment, the loader comprises a front loader, in which the extension arm is configured as the load arm of a front loader, which is capable of being varied via a first or a first and second hydraulic cylinder in respect of its angle of attack. A third hydraulic cylinder can be provided by means of which an implement provided on the extension arm, for example a loading shovel or a loading 
   In another embodiment, the loader comprises a front loader, in which the extension arm is configured as the load arm of the front loader, which is capable of being varied via a first or a first and second hydraulic cylinder in respect of its angle of attack. A third hydraulic cylinder can be provided by means of which an implement provided on the extension arm, for example a loading shovel or a loading fork, is capable of being caused to pivot. 
   Of course, all other customary loading implements, for example buckets, bale grabbers, etc., are capable of being used both with the telescopic loader and with the loader equipped with the front loader. 
   The sensor is preferably configured and arranged in such a way that a critical load condition on the loader is detectable. The sensor can be arranged on an axle of the vehicle, for example, and can indicate a critical load condition in the event of a correspondingly high, unbalanced load. Strain gauges or force transducers, for example, can find an application in this case. It is also conceivable to position the sensor at some other suitable point and, for example, to define the inclination of a vehicle frame in relation to the vehicle axis as the critical load condition quantity. 
   The invention and further advantages and advantageous further developments and embodiments of the invention are described in more detail and explained below with reference to the drawing which depicts illustrative embodiments of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawing: 
       FIG. 1  is a schematic right side view of a loader configured as a telescopic loader having a hydraulic arrangement; 
       FIG. 2  is a schematic circuit diagram of a hydraulic arrangement; 
       FIG. 2   a  is a schematic circuit diagram of an alternate embodiment of the hydraulic arrangement of  FIG. 2 , and 
       FIG. 3  is a schematic left side view of a loader exhibiting a front loader having a hydraulic arrangement. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Illustrated in  FIG. 1  is a loader  10  in the form of a telescopic loader. The telescopic loader  10  exhibits a frame  12 , to which an extension arm  14  is linked The frame  12  is supported by a front axle  16  and by a rear axle  18  with corresponding front and rear sets of wheels  20  and  22 , respectively. 
   The extension arm  14  is configured as a telescopic extension arm and is adjustably linked via a hydraulic cylinder  24  in respect of its angle of attack in relation to the frame  12 . A second hydraulic cylinder (not illustrated) is arranged in the interior of the extension arm  14  and permits the retraction and/or extension (telescoping) of the extension arm. A third hydraulic cylinder (not illustrated) is arranged on the free end of the extension arm  14  in the interior and permits the oscillation and/or tilting of a loading implement  26 . 
   The loader  10  possesses a hydraulic source  28  and a hydraulic tank  30 , which are arranged underneath the vehicle bodywork and serve the purpose of supplying the hydraulic components. 
   An operating device  34 , in the form of a hydro-mechanical joystick, is arranged in a cab  32  and serves the purpose of actuating the hydraulic components. The hydraulic components are illustrated substantially in  FIG. 2 . 
   A hydraulic arrangement  36  envisaged for the loader  10  is illustrated in  FIG. 2 . The hydraulic arrangement  36  comprises the hydraulic cylinder  24  and, should the need arise, the hydraulic cylinders (not illustrated) arranged for the telescoping of the extension arm  14  and tilting of the loading implement  26  the hydraulic cylinder  24  is connected via first and second supply lines  38  and  40 , respectively, to a hydraulically actuated control device  42 , via which the connection of the supply lines  38 ,  40  to the hydraulic pump  28  and the hydraulic tank  30  can be produced. 
   A load holding valve  44  is arranged in the supply line  40  associated with the chamber on the lifting side of the hydraulic cylinder  24 . The load holding valve comprises a pressure-limiting valve  46  capable of being opened via control pressure lines  48 ,  50 , which are connected to both supply lines  38 ,  40 , as well as a check valve  52  arranged in a bypass line and opening in the direction of the hydraulic cylinder  24 . The load holding valve  44  serves to ensure that, in the event of a pipe fracture on the lifting side of the hydraulic cylinder  24 , no hydraulic fluid is able to escape and the hydraulic cylinder  24  maintains its position. 
   The control device  42  comprises three gate positions, one for lifting, one for lowering and one more for holding the hydraulic cylinders. The control device  42  is configured as a hydraulically actuated proportional valve and can be hydraulically actuated or adjusted via corresponding control pressure lines  54 ,  56 . The control pressure in this case is generated by the hydro-mechanical operating device  34 , which is executed as a joystick. 
   The operating device  34  possesses valves  58 ,  60  that are actuated mechanically, for example, by moving the joystick, which provides for the engagement or disengagement of the hydraulic pump  28  with or from the control pressure lines  54 ,  56 . The mechanically actuated valves  58 ,  60  are preferably configured as pressure reduction valves. For example, a joystick or actuating lever present Oh the operating device  34  is pushed forwards, which results in the actuation of the valve  58 . The control pressure line  56  is then subjected to a hydraulic pressure produced by the hydraulic pump  28 , whereupon the control device  42  is displaced into its lifting position and the hydraulic cylinder  24  is filled with hydraulic fluid on the lifting side, that is to say it is extended. A corresponding actuation of the actuating lever in the opposite direction would cause actuation of the valve  60 , whereupon the control pressure line  54  would be filled with hydraulic fluid and the control device  42  would be displaced into the lowering position, that is to say the hydraulic cylinder  24  would be retracted. 
   In the illustrative embodiment depicted in  FIG. 2 , the control pressure line  54  is provided with an electro-hydraulic overpressure valve  62  connected to the hydraulic tank  30 . The overpressure valve  62  causes the control pressure prevailing in the control pressure line  54  to be reduced. In the event of a pre-set limit pressure being reached or exceeded by the control pressure, the overpressure valve  62  opens increasingly so that an increasing quantity of hydraulic fluid flows into the hydraulic tank  30 , with the result that the displacement of the control device  42  is reduced by the control pressure line  54  and, as a result, the actuation of the hydraulic cylinder  24 , in this case the retraction of the hydraulic cylinder  24 , is slowed down. Of course, the other control pressure line  56  can also be connected to an overpressure valve  62  of this kind. In this case, extension of the hydraulic cylinder  24  would then be slowed down. 
   Control of the overpressure valve  62  takes place through the electronic control unit  64 , which for its part receives control signals from the load case sensor  66 . Depending on the load condition, the sensor indicates a more or less critical load condition. As the critical load condition is approached, the control input transmitted by the electronic control unit  64  for adjusting the overpressure valve  62  is also strengthened, which then causes the valve to be increasingly opened, so that hydraulic fluid flows increasingly from the control pressure line  54  and the control pressure is reduced. The adjustment or the increase of the control input in this case preferably takes place proportionally to the signal provided by the sensor. 
   The load sensor  66  is preferably arranged on the rear axle  18  of the loader  10 . For example, the sensor  66  is configured as a strain gauge and registers or records the deflection of the rear axle  18 . It is then possible to arrive at a conclusion in respect of the application and removal of the load on the rear axle  18  from the signal values for the deflection. If the load on the rear axle  18  were to reduce increasingly, this can point to the existence of a critical load condition, namely at the latest if a load was no longer to be detected or indicated on the rear axle  18 . In this case, the loader  10  begins to overturn. A similar approach is also conceivable for the front axle  16 . 
   The illustrative embodiment depicted in  FIG. 2  provides a representative indication of the arrangement of only a single hydraulic cylinder  24 . As mentioned above, further hydraulic cylinders (not illustrated) can be used in parallel, which cylinders are capable of actuation in the same way as an actuating device  34  and are incorporated in a hydraulic arrangement  36  of the kind depicted in  FIG. 2 . 
   Furthermore, it is possible not only to restrict and/or to slow down the retraction of the hydraulic cylinder  24 . It is naturally also conceivable to restrict and/or slow down the extension, as would be required, for example, in order to avoid the extension of the extension arm  14  to prevent overturning of the telescopic loader. In this case, the control pressure line  56 , with which the lifting position of the control device  42  and with it the extension of the hydraulic cylinder  24  is actuated, would be provided with or connected to an electro-hydraulic overpressure valve  62 . 
     FIG. 2   a  depicts an alternate illustrative embodiment of the hydraulic arrangement, in which the control pressure line  54  is provided with an electro-hydraulic pressure reducing valve  62 ′, in conjunction with which the connecting line to the hydraulic tank  30 , which is provided in the illustrative example for  FIG. 2 , is omitted. Here, too, the pressure reduction valve  62 ′ causes the control pressure prevailing in the control pressure line  54  to be reduced or throttled. If a pre-set limit pressure is reached or exceeded by the control pressure, the pressure reduction valve  62 ′ closes so that the control pressure in the control pressure line  54  is reduced or throttled. If a pre-set limit pressure is reached or exceeded by the control pressure, the pressure reduction valve  62 ′ closes so that the control pressure in the control pressure line  54  reduces, with the result that the displacement of the control device  42  is reduced by the control pressure line  54  and, as a result, the actuation of the hydraulic cylinder  24 , in this case the retraction of the hydraulic cylinder  24 , is slowed down. Of course, the other control pressure line  56  can also be connected to a pressure reducing valve  62 ′ of this kind. In this case, extension of the hydraulic cylinder  24  would then be slowed down. 
   Here, too, control of the overpressure valve takes place through the electronic control unit  64 , which for its part receives control signals from a load case sensor  66 . Depending on the load condition, the sensor  66  indicates a more or less critical load condition. As the critical load condition is approached, the control input transmitted by the electronic control unit  64  for adjusting the pressure reduction valve  62 ′ is also strengthened, which valve is then closed increasingly, so that the control pressure reduces. The adjustment for the increase of the control input in this case preferably takes place proportionally to the signal provided by the sensor. 
   The load sensor  66  is preferably also located on the rear axle  18  of the loader  10 , in this case too, and is configured in an analogous manner to the illustrative embodiment depicted in  FIG. 2 . 
   The illustrative embodiment depicted in  FIG. 2   a  also provides a representative indication of the arrangement of only a single hydraulic cylinder  24 . In this case, too, further hydraulic cylinders (not illustrated) can be used in parallel, which cylinders are capable of actuation in the same way as an actuating device  34  and are also incorporated in a hydraulic arrangement  36  of the kind depicted in  FIG. 2   a . 
   Furthermore, it is possible not only to restrict and/or to slow down the extension, as would be required, for example, in order to avoid the extension of the extension arm  14  to prevent overturning of the telescopic loader. In this case, the control pressure line  56 , with which the lifting position of the control device  42  and with it the extension of the hydraulic cylinder  24  is actuated, would be provided with or connected to an electro-hydraulic pressure reduction valve  62 ′. 
     FIG. 3  depicts a loader  10  in the form of a tractor  68  with a front loader  70  as a further illustrative embodiment, in conjunction with which the same reference designations are used for the same components of the loaders  10 , such as the frame  12 , front axle  16 , rear axle  18 , wheels  20 ,  22 , loading implement  26  and cab  32 . 
   In this case, the load arms  72 , which are arranged to either side of the tractor  68 , represent an extension arm, the actuation of which in specific situations and in the event of overloading can give rise to critical load conditions of the loader  10 . 
   The hydraulic cylinders  74  provided for the actuation of the load arms  72  and the hydraulic cylinders  76  provided for the actuation of the loader implement  26  are operated in this case in an analogous manner to the hydraulic arrangement  36  depicted in  FIG. 2 . 
   Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.