Loader

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 hydraulically 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 actuating device is coupled for routing control pressure to the control device via first and second control pressure lines. An electronic control unit is connected for effecting operation of a control pressure control device, which is coupled to at least one of the control pressure lines, in response to a load signal received from the load sensor so as to actuate the control device for achieving a slowed-down actuation of the hydraulic cylinder in conjunction with the onset of a critical load condition. Thus, a restriction of a volumetric flow is achieved in at least one of the supply lines coupled to the hydraulic cylinder.

Description

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 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 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. 2a 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. 2a. 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 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 even 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 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.

Claims

1. In a loader including a frame supported on front and rear axles carrying front and rear sets of wheels, a hydraulically operated extension arm mounted to the frame for swinging vertically between lowered and raised positions, an extensible and retractable hydraulic cylinder coupled between said frame and said extension arm for selectively moving said arm between said lowered and raised positions, a first supply line coupled to a piston rod side of said hydraulic cylinder, a second supply line coupled to a piston side of said hydraulic cylinder, a pressurized hydraulic fluid source, a hydraulic fluid tank, at least one hydraulically switchable control device coupled, on the one hand, to said first and second supply lines and coupled, on the other hand, to said fluid source and fluid tank, a hydro-mechanical actuating device being coupled to said fluid source and said fluid tank and being coupled and selectively operable for routing a control pressure to said control device via first and second control pressure lines, so as to effect actuation of said control device for controlling the flow of hydraulic fluid to and from said hydraulic cylinder, a load sensor located on said loader for monitoring a load condition on the loader and operable for creating an electrical load signal representing said load condition, and an electronic control unit coupled to said load sensor for receiving said electrical signal and comparing it with a critical load stored in memory in said electronic control unit and for generating a control signal representing a difference between said load signal and said critical load, the improvement comprising: an electrically operable pressure controlling device being coupled to one of said control pressure lines, and further being coupled to said electronic control unit for receiving said control signal, whereby said pressure controlling device is operated in accordance with said control signal so as to effect changes in the pressure contained in said one control pressure line.

2. The loader, as defined in claim 1, wherein said pressure controlling device includes at least one electro-hydraulic overpressure valve capable of actuation by said electronic control unit and being coupled to said hydraulic tank so as to meter more or less fluid to said tank and in this way vary the pressure in said one control pressure line.

3. The loader, as defined in claim 1, wherein said pressure controlling device includes at least one electro-hydraulic pressure reduction valve capable of actuation by the electronic control unit and being coupled in said one control pressure line between said actuating device and said control device for varying the amount of pressure routed to said control device.

4. The loader, as defined in claim 1, wherein said actuating device includes one of a joystick or actuating lever.

5. The loader, as defined in claim 1, wherein said loader is a telescopic loader.

6. The loader, as defined in claim 1, wherein said loader is a front loader.

7. The loader, as defined in claim 1, wherein said load sensor is arranged on one of said front and rear axles.