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 FIGS. 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 FIGS. 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 38 envisaged for the loader 10 is illustrated in FIG. 2. The hydraulic arrangement 38 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, 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 cylinders. 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.
Patent Application
20080073155
