Abstract:
A loader includes a hydraulically operated extension arm, a load sensor for monitoring the load condition on the loader and a hydraulic arrangement for actuation of the extension arm and/or an implement attached to the extension arm. The hydraulic arrangement exhibits at least one hydraulic cylinder with one supply line on the piston rod side and one supply line on the piston side. At least one mechanically switchable control device is coupled between a source of fluid pressure and a hydraulic tank, on the one hand, and the supply lines on the other hand. An electronic control unit is connected for effecting operation of a restricting device coupled between the supply lines in response to a load signal received from the load sensor so as to achieve a slowed-down actuation of the hydraulic cylinder in conjunction with the on set of a critical load condition. Thus, a restriction of a volumetric flow is achieved in at least one of the supply line on the piston rod side or the supply line on the piston side of the hydraulic cylinder.

Description:
FIELD OF THE INVENTION 
     This 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 an implement attached to the extension arm, the hydraulic arrangement exhibiting at least one hydraulic cylinder with a first supply line on the piston rod side and a second supply line on the piston side, at least one mechanically switchable control device for controlling the at least one hydraulic cylinder, 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 systems with mechanically controlled control devices, in which the valve gates of the control device are actuated via Bowden cables or levers, the characterizing features disclosed in WO 2004/007339 A1 do not find an application, because it is not possible to intervene in a controlled manner by such simple means in the functions that are executed mechanically by the operator, 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 byway of introduction is configured in such a way that means for restricting the volumetric flow rate are provided between the control device and the hydraulic cylinder, by which means, depending on a sensor signal supplied by the sensor, a volumetric flow can be restricted in at least one of the supply line on the piston rod side or the supply line on the piston side of the hydraulic cylinder. The operability of the hydraulic cylinder actuated via a mechanically controlled control device is influenced via the means for varying the volumetric flow in such a way that a volumetric flow rate for the hydraulic fluid flowing into one of the two chambers of the hydraulic cylinder is restricted and/or reduced, so that the speed at which a specific quantity of hydraulic fluid flows into one of the chambers is restricted and/or reduced, and the movement of the hydraulic cylinder and/or piston is ultimately slowed down in this way. The volumetric flow of the hydraulic fluid flowing into the chamber of the hydraulic cylinder 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 over turning 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 restricting the volumetric flow rate preferably consists of at least one electro-hydraulic overpressure valve capable of actuation by the electronic control unit and is arranged in a connecting line extending between the supply line on the piston rod side and the supply line on the piston side. 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 valve is adjusted and/or the more the overpressure valve is opened. 
     A check valve is preferably provided in the connecting line, so that the hydraulic fluid is able to flow through the overpressure valve in only one direction from the supply line on the piston rod side into the supply line on the piston side, or vice versa. It Is also conceivable, however, for a check valve of this kind to be integrated already in the overpressure valve, in any case, the hydraulic cylinder can be actuated in this way in the opposite direction of movement from that which is customary. It is naturally also conceivable for a number of hydraulic cylinders to be capable of being used 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 over pressure valves can 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 the adjustment default, the extension arm is moving increasingly slowly until it comes to a halt. 
     In another embodiment, the means for restricting the volumetric flow also comprise at least one electro-hydraulic overpressure valve capable of being actuated by the electronic control unit, although the means are arranged in a discharge line branching from the supply line on the piston rod side or the supply line on the piston side of to the hydraulic tank. In this way, the hydraulic fluid branched through the overpressure valve from the supply line on the piston rod side or the supply line on the piston side is conveyed directly into the hydraulic tank, and not into the supply line on the piston side or the supply line on the piston rod side. This also permits smaller threshold pressure values to be set, since the pressure in the previous illustrative embodiment (connecting line) acting in the corresponding other supply line acts against the actual opening pressure, which has a negative effect on the sensitivity and/or on the response characteristic of the overpressure valve. This is not the case with an overpressure valve, which is arranged in a discharge line leading directly into the hydraulic tank. 
     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 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 the front loader, which is capable of being varied via a first or a first and a 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 for, is capable of being caused to pivot. 
     Of course, ail 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 pint and, fore 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 
         FIG. 1  is a schematic right side view of a loader configured as a telescopic loader having a hydraulic arrangement according to  FIG. 2  or  3 ; 
         FIG. 2  is a schematic circuit diagram of a hydraulic arrangement; 
         FIG. 3  is a schematic circuit diagram of an alternate hydraulic arrangement, and 
         FIG. 4  is a schematic left side view of a loader exhibiting a front loader having a hydraulic arrangement according to  FIG. 2  or  3 . 
     
    
    
     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 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 . 
     Referring now also to  FIGS. 2 and 3 , it can be seen that 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. 
     A mechanical operating device  34  arranged in the cab  32  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 and tilting of the loading implement. The hydraulic cylinder  24  is connected via a first supply line  38  and a second supply line  40  to a mechanically actuated control device  42 , here shown as a closed center, four way, three position directional control valve, via which the connection of the supply lines  38 ,  40  to the hydraulic pump  28  and the hydraulic tank  30  can be produced. The control device  42  is mechanically connected to the operating device  34 , for example via Bowden cables, so that displacement of the control device  42  and/or the valve gate of the control device  42  can be effected by moving the operating device  34 . 
     A toad holding valve  44  is arranged in the supply line  40  associated with the chamber of the lifting side of the hydraulic cylinder  24 . The load holding valve  44  comprises a pressure-limiting valve  46  capable of being opened in the direction of the control device  42 , which pressure-limiting valve is arranged in the supply line  40  and Is capable of being opened in the direction of the control device  42 , which pressure-limiting valve is arranged in the supply line  40  which is capable of being opened via control pressure contained in 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 cylinder. The control device  42  is configured as a mechanically switchable or mechanically actuated proportional valve and can be mechanically actuated or adjusted via an actuating device  54 , the actuating device  54  being mechanically connected to the operating device  34 . 
     The mechanically actuated control device  42  provides for the engagement or disengagement of the hydraulic pump  28  with or from the supply lines  38 ,  40 . For example, an actuating lever present on the operating device  34  is pushed forward, which results in the actuation of the control device  42 , and this 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 the displacement of the control device  42  into the lowering position, whereupon the hydraulic cylinder  24  would be retracted and the extension arm  14  lowered. 
     Provided in the illustrative embodiment depicted in  FIG. 2 , is a connecting line  56 , which extends between the two supply lines  38 ,  40 . Arranged in the connecting line  58  is a check valve  58  closing in the direction of the supply line  38  on the piston rod side, which check valve prevents hydraulic fluid from the supply line  40  on the piston side from flowing into the supply line  38  on the piston rod side. Arranged in the connecting line  56  between the check valve  58  and the supply line  38  on the piston rod side Is an electro-hydraulic over pressure valve  82 . The overpressure valve  62  is arranged in such a way that hydraulic fluid can flow from the supply line  38  on the piston rod side in the direction of the supply line  40  on the piston side. For this purpose, the electro-hydraulic overpressure valve  62  is connected to an electronic control unit  64 . As soon as a pressure limit pressure is reached by the pressure building up in the supply line  38  on the piston rod side, the overpressure valve  82  opens, so that hydraulic fluid flows into the supply line on the piston side and from there into the hydraulic tank  30 , with the result that the speed of displacement of the hydraulic cylinder  24  is reduced, because the volumetric flow rate of the hydraulic fluid present in the supply line  38  on the piston rod side is reduced. This means that the quantity of hydraulic fluid, which flows info the chamber of the hydraulic cylinder on the piston rod side, is reduced and, as a result, the actuation of the hydraulic cylinder  24 , in this case retracting the hydraulic cylinder  24 , is slowed down. Of course, the arrangement of the check valve  58  and the electro hydraulic overpressure valve  62  can be in the opposite sense, so that hydraulic fluid can flow from the supply line  40  on the piston side into the supply line  38  on the piston rod side. 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 a bad case sensor  66 . Depending on the load condition, the sensor  86  indicates a more or less critical load condition. As the critical load condition is approached, the control input transmitted by the electronic control unit  84  for adjusting the overpressure valve  82  is strengthened, which then causes the valve to be opened further, so that the discharge volumetric flow rate increases. The adjustment or the increase of the control input in this case preferably takes place proportionally to the signal provided by the sensor. 
     The 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 bad 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 conceivable for the front axle  16 . 
     Illustrated in  FIG. 3  is an alternate illustrative embodiment for a hydraulic arrangement  36 ′, in which there is arranged, in place of the connecting line  56  from  FIG. 2 , a discharge line  56 ′ in which the electro-hydraulic overpressure valve  62  is arranged. The discharge line  56 ′ branches from the supply line  38  on the piston rod side and passes into the hydraulic tank  30 . In this way, hydraulic fluid can flow directly from the supply line  38  on the piston rod side via the overpressure valve  62  into the hydraulic tank  30 . Control of the overpressure valve in this case takes place in an analogous manner to the illustrative embodiment depicted in  FIG. 2 . No check valve  58  is provided in the hydraulic arrangement  36 ′ depicted in  FIG. 3 , because no connection of the supply line  40  on the piston side to the discharge line  56 ′ is present. In an analogous manner to the illustrative embodiment depicted in  FIG. 2 , only the contraction of the hydraulic cylinder  24  is slowed down in  FIG. 3 . As in the illustrative embodiment described in relation to  FIG. 2 , it is also possible in the illustrative embodiment depicted in  FIG. 3  for the flow of hydraulic fluid to be provided from the supply line  40  on the piston side, and for the extension of the hydraulic cylinder  24  to be slowed down by this means. In this case, the discharge line  56 ′ is connected to the supply line  40  on the piston side, in conjunction with which the control of the overpressure valve takes place in an analogous manner to the example depicted in  FIG. 3 . 
     The illustrative embodiments of the hydraulic arrangements  36 ,  36 ′ depicted in  FIGS. 2 and 3  provide 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 also incorporated in the hydraulic arrangements  36 ,  36 ′ of the kind depicted in  FIGS. 2 and 3 . Furthermore, as already mentioned, it is possible not only to restrict and/or to slow down the retraction and/or lowering 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  in order to prevent overturning of the telescopic loader. In this case, for the illustrative embodiment in  FIG. 2 , the control pressure line  56 , with which the lilting 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 . For the illustrative embodiment in  FIG. 3 , the supply line  40  of the piston side would be connected to a corresponding discharge line  56 ′ with an electro-hydraulic overpressure valve  62 . 
       FIG. 4  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 loader  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  70 , 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  70  and the hydraulic cylinders  78  provided for the actuation of the loader implement  26  are operated in this case in an analogous manner to the hydraulic arrangements  36 ,  36 ′ depicted in  FIGS. 2 and 3 . 
     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.