Patent Publication Number: US-7712589-B2

Title: Device and method for braking the supporting booms of an earthmoving machine

Description:
FIELD OF THE INVENTION 
     The present invention relates to a device and method for braking the supporting booms of an earthmoving machine, for example an excavator, and a machine equipped with said device. 
     BACKGROUND OF THE INVENTION 
     Different types of earthmoving machines are known in the prior art, with different functions related to the type of performance and power required. For instance, there are single-boom or multi-boom excavators, depending on the number of knuckle booms which connect the bucket to the machine body. A multi-boom excavator generally allows more flexibility of use compared to the single-boom type. A multi-boom excavator is generally equipped with at least one specific knuckle between two consecutive booms having a supporting boom function, wherein the relative angle of inclination between the two booms is fixed during operation but can be adjusted—generally in a standstill position—by one or more positioning cylinders connected between the two booms operated by the operator. There is also an excavation boom to which the excavating bucket is attached; the angle of the bucket can usually be changed during the excavation operations. 
     A multi-boom excavator with more flexibility may give rise to reliability problems. In particular, the positioning cylinder operates as a large-sized sprag, since it must withstand a strong reaction force which can cause resistance problems in the cylinder supports, in the cylinder thereof, and in its lock valve, if any. The cylinder is strongly stressed because during particularly heavy-duty excavation operations—for example when working on hard ground—the pressure of the fluid inside of it may be very high, as it is proportional to the reaction force that the cylinder needs to exert to keep the two booms in a relative fixed position. In these conditions, the cylinder supports are subjected to high stress, so much so that it could even lead to their rupture. 
     SUMMARY OF THE INVENTION 
     Therefore, the purpose of the present invention is to solve the above-mentioned problems and to propose a device and method for braking the supporting booms of an earthmoving machine, for example an excavator, and a machine equipped with said device, capable of reducing the reaction force of the positioning cylinders. The reduction of the reaction force of the positioning cylinder is achieved, according to the present invention, via a braking system applied between two supporting booms which is operated during the time in which the positioning cylinder remains inactive—hence the angle between the two booms remains fixed—during the excavation operations, thereby unloading part of the reaction force of the cylinder, hence reducing the stress. 
     The system described above creates a stall torque relative to the pivot between the two booms, which transfers a part of the reaction onto the braking element thereof. The induced pressure of the fluid inside the positioning cylinder is advantageously used for operating the braking system. Therefore, the present invention relates to a device for braking the supporting booms of an earthmoving machine, said machine equipped with two or more supporting booms, interconnected by pivoting points, and one or more positioning cylinders capable of determining the relative angular position of said supporting booms, characterized in that it comprises one or more braking systems applied to said supporting booms, capable of exerting a braking action on said supporting booms during a time in which the said one or more positioning cylinders remain inactive. 
     The present invention relates particularly to a device and method for braking the supporting booms of an earthmoving machine, for example an excavator, and a machine equipped with said device, as described more fully in the claims, which are an integral part of this description. 
     The purposes and advantages of this invention will become clear from the following detailed description of a preferred embodiment, and the relative alternative forms of embodiment, and the drawings that are attached hereto, which are merely illustrative and not limitative. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  describes an excavator equipped with three booms, wherein a braking device is applied in accordance with the present invention. 
         FIG. 2  shows an enlargement of the detail in which the braking system is applied to the excavator. 
         FIGS. 3 and 4  show an exemplary embodiment of a part of the braking device comprising a brake disk in exploded and enlarged views of the components, respectively. 
         FIGS. 5 and 6  show an exemplary embodiment of a part of the braking device comprising a brake caliper in exploded and enlarged views of the components, respectively. 
         FIG. 7  shows an exemplary embodiment of the brake caliper in exploded view of the components. 
         FIG. 8  shows an exemplary embodiment of a hydraulic circuit capable of controlling the operation of the braking system. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     In the drawings the same reference numbers and letters are used to identify the same elements.  FIG. 1  shows an example of a three-boom excavator, wherein a first boom  1  and a second boom  2  are the supporting booms, whereas a third one  3  serves as an excavating boom which is connected to a bucket  4 . 
     There is a positioning cylinder  5  connected between the first boom  1  and the second boom  2 , pivoted to the end  51  of the first boom connected to the excavator, and to the end  52  of the second boom opposite the connection of the third boom, respectively, near the pivot  6  between the two booms. The positioning cylinder  5  is operated by the operator in order to determine the angle between the two supporting booms  1  and  2 . This angle generally remains fixed during the excavation operations. Hence, according to the present invention, a braking system  7  is achieved, for example, at the extension part of the first boom  1 , as shown in the dotted circle in  FIG. 1 , enlarged in  FIG. 2 . 
     The braking system  7  produces a reactive torque relative to the pivot  6  between the two booms, which makes it possible to reduce the stress on the positioning cylinder to a typical value of 30%. 
     In a possible embodiment, as also shown in  FIGS. 3 and 4 , the braking system consists of a disk brake, comprising a rigid support  8  to which two brake disks  9  and  10  are fixed, for example with screws, at the two side surfaces. The rigid support  8  is shaped as a rigid forked extension part of the first boom  1  relative to the pivot  6 . 
       FIGS. 5 and 6  show another component of the braking system, which consists of a brake caliper  11  which is wound around the brake disks (as shown in  FIG. 2 ). The brake caliper  11  is fixed to the second boom  2  with two supports,  12  and  13 , in order to keep it in a fixed, longitudinal position relative to the second boom—but floating crosswise relative to the second boom—around the disks. As a matter of fact, the two supports  12  and  13  comprise pivots  121  and  131 , respectively, fitted into their holes,  122  and  132 , drilled at the ends of the caliper  11 , which allow the caliper to slide sideways. By doing so, the side clearances of the caliper—generated under the braking action—will be taken up with respect to the brake disk, thereby preventing the caliper from producing side thrusts on the disk. There may be several holes ( 122  or  132 ) on the same side in order to adjust the crosswise position of the caliper relative to the second boom. 
     The rigid extension  8  of the disk brake is achieved with an angle which makes it possible to work with the caliper  11  (fixed to the second boom) at all possible angles between the two booms. 
       FIG. 7  shows an exploded view of the caliper  11 , showing its possible embodiment, in which there are two pads  14  and  15  inside the caliper, capable of pressing against the brake disks  9  and  10  ( FIG. 2 ), via the force exerted by two pistons  16  and  17  inserted in one side of the caliper—in a suitable recess—and controlled by the brake fluid circuit. The caliper casing is actually in one piece, shown in two parts in exploded view in order to show its internal components. 
     With reference to  FIG. 8 , as far as the fluid circuit control is concerned, a check valve  20  is used for supplying, in a way in itself known, the ends of the positioning cylinder  5 —which are provided with inlet points for the fluid inside the cylinder—with hydraulic pressure via two fluid lines, in order to adjust the cylinder elongation according to the command given by the operator via a pilot valve  21 . By doing so, induced pressures are generated in the fluid circuits of the cylinder and are used for operating the braking system. The pressurized fluid of the two lines is also directed in parallel to a bistable shuttle sector valve  22  which transfers the inlet fluid pressure having the highest value between the two lines, to the outlet. The valve outlet  22  is directed to the inlet of a brake release valve  23  which sends the pressurized fluid to the pistons of the brake caliper  11 . Therefore, the induced pressure on the positioning cylinder  5  is shared with the braking system  7 . The braking pressure—which, for that matter, is equal to the induced pressure in the positioning cylinder—is proportional to the load on the cylinder and can reach extremely high values, even up to 800 bars or more. 
     In order to operate the positioning cylinder so that the elongation can be changed, thus changing the angle between the two supporting booms  1  and  2 , the release valve  23  is operated by activating the check valve  20 , directed to a control inlet of the release valve  23  via a second sector valve  24 , which opens the release valve and releases its fluid overpressure into a fluid containment tank TNK. By doing so, the braking system opens up, thereby operating the positioning cylinder, in order to change the angle between the two booms  1  and  2 . 
     Therefore, the braking method related to this invention involves:
         using the induced pressure in the positioning cylinder to operate a braking system set between the two supporting booms;   keeping the braking system braked during the time in which the positioning cylinder is kept inactive in a fixed position;   opening the braking system when the elongation of the positioning cylinder must be changed.       

     Since the braking system pads press against the disks without sliding, thereby minimizing their wear, it is advantageously possible to have them both (pads and disks) made of steel (inexpensive and capable of withstanding high pressures) so that it will not be necessary to replace them throughout the whole lifetime of the machine. 
     All hydraulic circuit valves may be of any known type, as long as their dimensions are suitable for their intended purpose, according to the power of the machine. 
     It will be apparent to the person skilled in the art that other alternative and equivalent embodiments of the invention can be conceived and reduced to practice without departing from the true spirit of the invention. In the case of an excavator equipped with extra supporting booms, wherein there are more than two supporting booms, a braking system may be required for each positioning joint. 
     The positions of the disks and calipers may be reversed on different booms: brake disk on the first boom and caliper on the second boom, as described in the previous example, or brake disk on the second boom and caliper on the first boom. Brake disks may be provided on both sides of one or more supporting booms. Different conformations of the rigid extension part  8  as well as different positioning points on the supporting boom are possible. 
     There may also be machines equipped with more than one cylinder, typically two on the two sides of the first boom, at the front or rear side relative to the elongation of the excavator booms. However, any angular position of the extension which carries the brake disk relative to the pivot between the two supporting booms is possible, depending on the position of the brake caliper and of the positioning cylinder (or cylinders), thereby preventing them from interfering with each other. 
     It is possible to use drum brakes instead of disk brakes, with per se known installation methods. 
     The advantages in connection with the use of this invention are clear. The braking system subject of this invention reduces the load on the positioning cylinder by a typical value of 30%, hence increasing the operating capacity of the machine when in specific heavy-duty excavation conditions. 
     The hydraulic capacity limitations during the lifting phase occurs for higher reaction force values, with an increase in the lifting capacity. 
     The braking system can also be installed after purchasing the machine, hence supplied as an additional option. 
     Given the same total reaction force required by the machine, the installation of the braking system provides for the possibility to reduce the dimensions, hence the cost of the positioning cylinder. 
     The braking system reduces the risk of damaging the supports of the positioning cylinder, thus reducing the reaction force on it. 
     From the description set forth above it will be possible for the person skilled in the art to embody the scope of the invention without introducing any further construction details.