Patent Publication Number: US-6705595-B2

Title: Heavy vehicle lifting device and method

Description:
This application is a divisional of U.S. application Ser. No. 09/235,305 filed Jan. 22, 1999, now U.S. Pat. No. 6,193,219 which is a continuation of PCT/CA98/00496 filed May 22, 1998 designating the United States and claiming priority of Canadian Patent Application serial number 2,206,010 filed May 23, 1997. 
    
    
     TECHNICAL FIELD 
     The present invention relates to lifting mechanisms and, more particularly, to a lifting device which is adapted to elevate the revolving frame of a heavy mechanical shovel from its wheeled undercarriage. 
     BACKGROUND ART 
     Heavy vehicles, such as bucket wheel excavators or mechanical shovels, are subject to maintenance or repair work as, for instance, repairs to the ring gear of the turntable of a mechanical shovel which require that the revolving frame thereof, i.e. the upper part of the mechanical shovel, be lifted so as to disengage the same from the shaft gudgeon which extends at right angle from the center of the ring gear of the carbody, i.e. the lower part or undercarriage of the mechanical shovel. Accordingly, in a conventional method for lifting the revolving frame of a given mechanical shovel, a number of short stroke jacks mounted on steel support members are first disposed at the rear and at the front of the aforementioned mechanical shovel and, more particularly, under opposite ends of the revolving frame thereof. After an initial extension of the short stroke jacks, wood blocks are disposed at the rear and at the front of the revolving frame to thus hold up in position the revolving frame while the short stroke jacks are retracted and mounted on other wood blocks for a second lifting operation. Due to the short stroke of the jacks, the overall lifting operation is made in several steps, i.e. in a series of successive short lifting operations, and requires continuous provision of wood blocks. 
     With this method, it takes up to six days for lifting and lowering a large mechanical shovel. Moreover, the operators must work under the load during the lifting operation and there is thus a significant risk of accident, for instance, because this method does not provide a high degree of stability (e.g. the wood blocks can sometimes yield or at least be crushed under the high load being lifted). It is also noted that for some specific models of mechanical shovels (less than 600 tons), a 150-ton crane was used to lift the front portion of the revolving frame with a pair of 200-ton jacks being used at its rear portion. Consequently, a great portion of space available in the workshop was taken by the crane which also was mobilized for a number of days. 
     Furthermore, the above method cannot be used outside of the workshop since it is not adapted to compensate for the packing soil effect which could occur at the lifting point during the lifting operation of such heavy mechanical shovels. 
     DISCLOSURE OF INVENTION 
     It is therefore an aim of the present invention to provide a lifting device and method adapted to ensure the safe lifting of heavy equipment, such as the mechanical shovels used in the mining industry. 
     It is also an aim of the present invention to provide a lifting device which is adapted to increase the speed of the lifting operation. 
     It is a further aim of the present invention to provide such a lifting device which is designed for offering ease of assembly and disassembly. It is a still further aim of the present invention to provide a shovel lifting device which is adapted for lifting different models of shovels. 
     It is a still further aim of the present invention to provide a shovel lifting device which is easy to transport. 
     It is a still further aim of the present invention to provide a lifting device which can be used in or outside of a workshop. 
     Therefore, in accordance with the present invention, there is provided a shovel lifting device comprising front and rear lifting beams which are adapted to support the revolving frame of a given mechanical shovel, front and rear lifting means respectively adapted to control the vertical displacement of said front and rear lifting beams, said front and rear lifting means, when taken as a whole, comprising at least three lifting means, and connection means interconnecting said front and said rear lifting beams with said corresponding lifting means, whereby said revolving frame of said mechanical shovel can be lifted by operation of said lifting means of said shovel lifting device. 
     Also in accordance with the present invention, there is provided a shovel lifting device comprising a front and a rear lifting beams, each said front and said rear lifting beams being provided with at least one bracket means which is adapted to cooperate with a mechanical shovel having an upper part and a lower part to ensure a proper positioning of said front and said rear lifting beams with respect to said mechanical shovel, front and rear lifting means adapted to control the vertical displacement of said front and said rear lifting beam, wherein said front and said rear lifting beam comprise at least three lifting means, whereby said upper part of the shovel can be lifted by operation of said lifting means of said shovel lifting device 
     Further in accordance with the present invention, there is provided a method of lifting heavy mechanical shovel using a shovel lifting device having front and rear lifting beam which are adapted to support the revolving frame of a given mechanical shovel, front and rear lifting means respectively adapted to control the vertical displacement of said front and rear lifting beam, wherein said front and rear lifting means, when taken as a whole, comprising at least three lifting means, the method comprising the following steps: 
     a) preparing a lifting area and the mechanical shovel; 
     b) installing said rear and said front lifting beams with said corresponding lifting means thereof at the appropriate location with respect to the mechanical shovel; and 
     c) lifting the mechanical shovel in a single step by operation of said lifting means. 
     Still further in accordance with the present invention, there is provided a method of lifting heavy mechanical shovel using a shovel lifting device having front and rear lifting beam which are adapted to support the revolving frame of a given mechanical shovel, front and rear lifting means respectively adapted to control the vertical displacement of said front and rear lifting beam, wherein said front and rear lifting means, when taken as a whole, comprising at least three lifting means, said lifting means being provided with detector means which are adapted to determine the length stroke and/or the absolute lifting elevation of the mechanical shovel at each of said lifting means, the method comprising the following steps: 
     a) preparing a lifting area and the mechanical shovel; 
     b) installing said rear and said front lifting beams with said corresponding lifting means thereof at the appropriate location with respect to the mechanical shovel; 
     c) mounting said detector means to said lifting means; 
     d) recording the reference lifting plan; and 
     e) lifting the mechanical shovel by operation of said lifting means. 
     Still further in accordance with the present invention, there is provided a method of lifting heavy mechanical shovel using a shovel lifting device comprising two lifting beams, removable bracket means being adapted to be mounted to said lifting beams, front and rear lifting means respectively adapted to control the vertical displacement of said front and rear lifting beam, said front and rear lifting means comprising at all at least three lifting means, said lifting means being provided with removable detector means which are adapted to determine the length stroke and/or the absolute lifting elevation of the mechanical shovel at each of said lifting means, the method comprising the following steps: 
     a) preparing a lifting area and the mechanical shovel; 
     b) if required, mounting said removable bracket means associated with the mechanical shovel to be lifted to said lifting beams; 
     c) installing said rear and said front lifting beams with said corresponding lifting means thereof at the appropriate location with respect of the mechanical shovel; 
     d) mounting said detector means to said lifting means; 
     e) recording the reference lifting plan; and 
     f) lifting the mechanical shovel by operation of said lifting means. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, showing by way of illustration a preferred embodiment thereof and in which: 
     FIG. 1 is a perspective view taken at a slight angle to the horizontal of a shovel lifting device in accordance with the present invention shown in the process of lifting the revolving frame of a large mechanical shovel which is shown in broken lines; 
     FIG. 2 is a partly exploded perspective view of a front lifting assembly comprised of a pair of front lifting units and a front lifting beam of the device of FIG. 1; 
     FIG. 3 is a partly exploded perspective view of a rear lifting assembly comprised of a pair of rear lifting units and a rear lifting beam of the device of FIG. 1; 
     FIG. 4 is a partly exploded perspective view of the front lifting assembly with a spacing block mounted on each front lifting units; 
     FIG. 5 is a front elevational view partly in cross-section of a pair of front cylinders, a front base structure and a front mounting box of one of the front lifting units; 
     FIG. 6 is a vertical cross-sectional view of one of the front cylinders; 
     FIG. 7 is a front elevational view partly in cross-section of a pair of rear cylinders, a rear base structure and a rear mounting box of one of the rear lifting units; 
     FIG. 8 is a vertical cross-sectional view of one of the rear cylinders; 
     FIG. 9 is a cross-sectional view of the front lifting beam illustrating how the lifting arms thereof secure the front lifting beam to the revolving frame of the mechanical shovel; 
     FIG. 10 is a cross-sectional view of the front lifting beam and of its moveable hook assembly which illustrates how the front lifting beam can be secured to the revolving frames of a different mechanical shovel, two such other shovels being herein shown; 
     FIG. 11 is a top plan view of a horizontal bracket which is removably mounted to the rear lifting beam; 
     FIG. 12 is a cross-sectional view taken along lines  12 — 12  of FIG.  11  and showing the horizontal bracket which is removably mounted to the rear lifting beam; 
     FIG. 13 is a top plan view of an inclined bracket which is removably mounted to the rear lifting beam; 
     FIG. 14 is a cross-sectional view taken along lines  14 — 14  of FIG.  13  and showing the inclined bracket which is removably mounted to the rear lifting beam; and 
     FIGS. 15 and 16 are perspective and elevational views of an alternate embodiment of the lifting arm. 
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     In accordance with the present invention, FIG. 1 illustrates a shovel lifting device  10  which is used to lift the revolving frame F of a mechanical shovel so as to disengage the revolving frame F from the shaft gudgeon which extends at right angle from the center of the ring gear of the undercarriage or carbody C of the shovel to allow for repairs thereof. 
     More specifically, the shovel lifting device  10  includes two front lifting units  12  and two rear lifting units  14  which are respectively located at opposed ends of front and rear lifting beams  16  and  18  which are adapted to be secured respectively under the front and rear ends of the revolving frame F of a given mechanical shovel. The shovel lifting device  10  further includes an hydraulic control unit (not shown) which is located outside of an established security perimeter to eliminate the necessity of having operators under or near the load during the lifting operation. Therefore, the chances of accident during the operation of the shovel lifting device  10  are greatly reduced. 
     It is seen from FIGS. 5 and 7 that each front lifting units  12  includes a pair of front hydraulic cylinders  20  which are connected in a parallel fashion. Similarly, each rear lifting unit  14  includes a pair of parallel rear hydraulic cylinders  22 . Each front and rear cylinder  20  and  22  of a pair of cylinders is adapted for retaining the load in the event of a failure of the other front or rear cylinder  20  and  22  of the same pair. It is noted that the front and the rear cylinders  20  and  22  have all the same stroke and that they include an outer square casing  24  and  26 , respectively, which is slidably mounted on an inner casing  28  and  30  of an annular cross section. As illustrated in FIG. 7, each outer square casing  26  includes two self lubricating bearings  32 . Each such bearing  32  comprises four plates  34  which are each provided with an hydraulic lubricator  36  and which each have an inner arched side. These plates  34  are mounted to the four inner sides of the outer square casing  24  and  26  so as to define a circular opening which generally corresponds to the outside diameter of the inner casing  28  and  30 . 
     This allows for a proper relative telescopic motion between the outer square tubular casings  24  and  26  and the inner casings  28  and  30 . This double casing configuration, i.e. each outer square casing  24  and  26  with its respective inner casing  28  and  30 , provides a better resistance to lateral loads which may be induced either by the load supported by the front and rear beams  16  and  18  or by the wind and the packing soil effect when the shovel lifting device  10  is used outside of the workshop. It is noted that the double hydraulic cylinder configuration of each front and rear lifting units  12  and  14  also contributes to improve the side load capacity of the overall shovel lifting device  10 . 
     A safety valve (not shown) is mounted at the inlet of each front and rear cylinders  20  and  22  to ensure that the load will be held up in the event of an accidental loss of pressure in the hydraulic circuit. Each safety valve is accessible via an opening  40  defined in the casing of each front and rear cylinders  20  and  22 . This opening  40  is provided with a bolted plate  42  through which extend the feed and return flexible conduits  44  which are used to connect each front and rear cylinder  20  and  22  to the hydraulic control unit (not shown). As best seen in FIG. 5, the flexible conduits  44  are secured on the side of each outer square casing  24  and  26  and are provided at the bottom thereof with an oil flow indicator  46  which allows for visual inspection of the flow of oil leaving each front and rear cylinder  20  and  22 . 
     More particularly, each pair of front cylinders  20  is respectively mounted at the bottom end thereof to a front base structure  48  and at the upper end thereof to a front mounting box  50  to ensure the stability of the shovel lifting device  10  and to allow for the joint operation of the front cylinders  20  of each front lifting unit  12 . As seen in FIGS. 5 and 6, the front cylinders  20  of each front lifting unit  12  are each secured to the front base structure  48  by means of a coupling pin  52  which is introduced in openings  54  defined in the front base structure  48  and in the hole (not shown) extending through the bottom end of the inner circular casing  28  of each front cylinder  20 . 
     As shown in FIGS. 2,  5  and  6 , the front mounting box  50  includes a head plate  56 , two side plates  58  extending at right angles from the underside of the head plate  56  and a mounting plate  60  which is welded to the back edge of the head plate  56  and to the side plates  58 . The underside of the head plate  56  is provided with two cylindrical protuberances  62  having respective coaxial recesses  64  which receive the head of the pistons of a given pair of front cylinders  20 . As best seen in FIGS. 5 and 6, the mounting plate  60  of the front mounting box  50  is bolted to mounting plates  66  which extend at right angles from the outer square casing  24  of the front cylinders  20  to thus secure each front mounting box  50  to its corresponding pair of front cylinders  20 . Therefore, once the front mounting boxes  50  have been mounted on the head of the pistons of the front cylinders  20  and secured to their corresponding outer square casings  24 , the latter can be moved by operation of the front cylinders  20  associated therewith. Moreover, each front lifting unit  12  can be handled as an integral assembly, for instance (when possible), by a forklift which engages fork receiving openings  67  extending horizontally on the exterior surface of both outer square casings  24  of each pair of front cylinders  20 . 
     In some cases, a spacing block  68 , such as the one illustrated in FIG. 4, needs to be mounted on the head plate  56  of the front mounting box  50  of each front lifting units  12  in order to compensate for lost motion in the stroke of the front cylinders  20  depending on the model of mechanical shovel being lifted. Indeed, some models of mechanical shovels, for instance the P&amp;H 2100 BLE and 2300 XPA, are provided with front and rear supporting points which are not at the same elevation. More particularly, for these models of shovels, the rear supporting points to which the rear lifting beam  18  is in contact with are at a lower elevation than the front supporting points to which the front lifting beam  16  is anchored and, since the front and the rear cylinders  20  and  22  have the same stroke, a preliminary extension of the front cylinders  20  is required and thus the stroke of the front cylinders  20  which is available for the lifting operation of the mechanical shovel is reduced. Therefore, the spacing block  68  is used to compensate the difference in heights that exists between the front and the rear supporting points of some mechanical shovels and thus allows for a fill use of the available stroke of the front cylinders  20  for the lifting operation. It is noted that the spacing blocks  68  are not required when the difference in height between the front and the rear supporting points of the mechanical shovel does not constitute an obstacle to the disengagement of the shaft gudgeon from the revolving frame F of the shovel, that is to say that the available length of stroke of the front cylinders  20  is sufficient enough to ensure that the carbody C is totally disengaged from the revolving frame F of the mechanical shovel and thus allows for the displacement of the carbody C. 
     With reference to FIG. 2, each spacing block  68  comprises a bottom plate  70 , two side walls  72  extending at right angles therefrom, a top plate  74  and a beam mounting plate  76 . The spacing block  68  further comprises two vertical reinforcement plates  78  which extend between the bottom  70  and the top plates  74  and three horizontal reinforcement plates  80  which extend between the side walls  72  and the vertical reinforcement plates  78  to ensure a proper resistance to side loads. The bottom plate  70  of each spacing block  68  is bolted to the head plate  56  of each front mounting box  50 . 
     Therefore, depending on whether or not the spacing block  68  is required, the front lifting beam  16  will be mounted to the beam mounting plate  76  of each spacing block  68  or to the mounting plate  60  of each front mounting box  50 . Indeed, the front lifting beam  16  is provided at each end thereof with a beam connection member  82  which is adapted to secure the front lifting beam  16  to each front lifting point  12  so that the front lifting beam  16  will be raised or lowered by operation of each pair of front cylinders  20 . With reference to FIGS. 2 and 4, each beam connection member  82  of the front lifting beam  16  includes a mounting plate  84  having front and rear surfaces  86  and  88  and a bolting pattern which corresponds to the bolting pattern of either the beam mounting plate  76  of the spacing blocks  68  or the mounting plate  60  of the front mounting boxes  50 . Each beam connection member  82  of the front lifting beam  16  also includes two side walls  90  which extend at right angles from the periphery of the front surface  86  of the aforementioned mounting plate  84 , the side wall  90  being adapted to receive either the side walls  72  of the spacing block  68  or the side plates  58  of the front mounting box  50 . Each beam connection member  82  further includes two lateral beam supporting plates  92  and two lower beam supporting plates  94  extending at right angles from the rear surface  88  of the mounting plate  84  and being adapted to receive one end of the front lifting beam  16 . Therefore, each end of the front lifting beam  16  is introduced between the two lateral beam supporting plates  92  so as to be supported at their lower comers by the two lower beam supporting plates  94 . Thereafter, each end of the front lifting beam  16  is secured to its associated beam connection member  82 . In order to reinforce the lateral support offered by the two lateral beam supporting plates  92 , four plates  96  are welded to the corresponding edges of each lateral beam supporting plate  92 . The lateral support is also reinforced by two horizontal plates  98  extending from the rear surface  88  of the mounting plate  84  and on the outside of each lateral beam supporting plate  92 , the plates  98  extending at right angles to each lateral beam supporting plate  92  of the beam connection member  82  and to the rear surface  88  of the mounting plate  84 . Each beam connection member  82  of the front lifting beam  16  further includes a top member  100  provided with two lugs  102  which may be used to handle the front lifting beam  16 , for instance with a crane. 
     Now referring to FIGS. 2 and 9, the front lifting beam  16  consists of a bottom plate  104 , a front plate  106 , a rear plate  108  and a top plate  110  all welded together so as to form a rectangular tubular beam. The bottom plate  104 , the front plate  106 , the rear plate  108  and the top plate  110  are all 1½ inch thick and made of steel. The exterior sides of the bottom and top plates  104  and  110  are each lined throughout their length with a reinforcement plate  112  having a thickness of one inch. Four reinforcement plates  114  extending at right angles between the inside surface of the top  110 , the bottom  104 , the front  106  and the rear plates  108  are uniformly distributed along the length of the front lifting beam  16  to improve the resistance thereof to torsion. Two fork receiving openings  116  are provided on the reinforcement plate  112  of the bottom plate  104  for handling purposes of the front lifting beam  16 . 
     As best seen in FIGS. 2,  4  and  9 , the front lifting beam  16  is also provided with a pair of lifting arms  118  which are adapted to secure the front lifting beam  16  to different models of mechanical shovels. Each lifting arm includes a pair of spaced apart L-shaped plates  120  which are welded to the exterior surface of the rear plate  108  and to the reinforcement plate  112  of the bottom plate  104 . The front portion of each pair of L-shaped plates  120  extends through the square notch  122  defined at the bottom of a plate  124  which is welded to the front plate  106  of the front lifting beam  16  and to which a rectangular plate  126  is also welded. 
     As shown in FIG. 10, a moveable hook assembly  128  mounted between the L-shaped plates  120  of each lifting arm  118  includes a hook  130  which is moveable within a guide casing  132  by operation of a bolt  134  which is mounted to a rear plate  136  of the guide casing  132  and to the hook  130  itself. Therefore, the hook assemblies  128  are used to secure the front lifting beam  16  to the bottom plate of the revolving frame F′ of certain types of shovels, such as the P&amp;H 2300 XPA shovel. It is noted that, in FIG. 9, the same side of the front lifting beam  16  is used for the lifting operation of the P&amp;H  2100  BLE shovel, but that no moveable hook assemblies  128  are required in the case of the shovel of FIG.  9 . 
     In the case of the model of mechanical shovel of FIG. 9, the attachment of the front lifting beam  16  is ensured by way of two pairs of spaced apart lugs  138 , also referred to as supporting points, welded on the underside of the revolving frame F of the mechanical shovel and which are adapted to be introduced between each corresponding lifting arm  118  so that the lugs  138  will be aligned with openings  140  defined in the front portion of each pair of L-shaped plates  120  for allowing for the insertion of coupling pins  142 . It is also noted that two spacing plates  144 , one for each lifting arm  118  and having a thickness of 6 inches, are required to ensure the positioning and the support of the front lifting beam  16  on the front of the P&amp;H 2100 BLE shovel of FIG.  9 . More particularly, each spacing plate  144  is supported at the bottom thereof by the top of the guide casing  132 . 
     Finally, the revolving frame F″ (see FIG. 10) of the B-E 295BI and 295BII shovel models are mounted in the same manner as the P&amp;H 2100 BLE of FIG. 9, but in this case, to the rear side of the front lifting beam  16  and, more particularly, to the rear portion of the L-shaped plates  120 , as illustrated in FIG.  10 . It easily seen that the front lifting beam  16  is secured to these models of mechanical shovels by means of lugs  146  and coupling pins  148 . However, the B-E 295 BI and 295BII models require the use of wedges  150  to fill the space between the top surface of the front lifting beam  16  and the underside of the revolving frame F″ of the shovel to provide an appropriate supporting surface once the front lifting beam  16  has been positioned. This will thus contribute to ensure that the lifting surface is level and that no shearing stress is induced on the coupling pins  148  during the lifting operation. 
     As previously mentioned, the rear lifting units  14  are similar to the front lifting units  12  in that each rear lifting unit  14  is formed of a pair of rear cylinders  22 , each rear cylinder  22  being provided with an outer square casing  26  which is slidably mounted on an inner casing  30  having a circular cross section. However, the rear cylinders  22  are adapted to support and lift bigger loads than the front ones. For instance, the front and rear lifting beams  16  and  18 , respectively, have respective capacities of 150 tons and 500 tons, with the rear lifting beam  18  being positioned slightly in front of the shovel&#39;s counterweight, whereby counterbalancing principles are used to reduce the load on the front lifting beam  16 . Thus, the lifting capacity required to lift a mechanical shovel is greater at the rear than at the front thereof. 
     Accordingly, the front and rear cylinders  20  and  22  are respectively 9 and 12½ inches in diameter and have a 66-inch stroke. Moreover, as shown in FIGS. 7 and 8, the inner casing  30  of each rear cylinder  22  is provided at the lower end thereof with a flange  152  which has eight screw holes  154  uniformly distributed on the periphery thereof for mounting each rear cylinder  22  to its corresponding rear base structure  156 . The rear base structure  156  of each rear lifting units  14  is provided with two fork receiving openings  158  for handling purposes. Therefore, when each pair of rear cylinders  22  has been mounted to its respective rear base structure  156 , both rear lifting units  18  can be handled by the fork openings  158  defined in the rear base structures  156 . As best seen in FIGS. 7 and 8, each outer square casing  26  is provided at an upper end thereof with a plurality of peripheral connection plates  160  having holes  162  which correspond to the screw holes defined in the flanges  166  of both cylindrical protuberances  168  extending downwardly from the head plate  170  of each rear mounting box  172 . Therefore, as for the front lifting units  12 , a rear mounting box  172  is mounted on each pair of rear cylinders  22 . The rear mounting boxes  172  are quite similar to the front ones in that they comprise a head plate  170 , two side plates  174  extending laterally from the underside of the head plate  170  and a mounting plate  176  extending at right angles from the head plate  170  between the two side plates  174 , the mounting plate  176  being adapted to cooperate with the mounting plates  178  extending at right angles from the exterior surface of each outer square casing  26  and with the beam connection members  180  of the rear lifting beam  18 . The side plates  174  of the rear mounting boxes  172  are strengthened by horizontal and vertical reinforcement plates  182  mounted thereon. As mentioned above, the head plate  170  of each rear mounting box  172  is provided with two cylindrical protuberances  168 , each protuberance  168  having a circular recess  184  for receiving the head of the piston of a given rear cylinder  22  and having a transversal hole  186  which is adapted to be aligned with the hole defined in the head of each piston  190  to allow for the insertion of a coupling pin  192 . Therefore, once the rear mounting box  172  has been properly mounted to the head of both pistons  190  of a given pair of rear cylinders  22  and to the outer square casings  26  associated therewith, the latter can be displaced by operation of the rear cylinders  22 . 
     It is seen from FIG. 2 that, like the front lifting beam  16 , the rear lifting beam  18  is provided at each end thereof with a beam connection member  180  which includes a mounting plate  194  having front and rear surfaces  196  and  198  and which defines a bolting pattern corresponding to the bolting pattern of the mounting plate  176  of the rear mounting boxes  172 . This ensures an easy and quick mounting of the rear lifting beam  18  to both rear lifting units  14 . The beam connection members  180  of the rear lifting beam  18  further each include two side walls  200  which extend laterally from the front surface  196  of the mounting plate  194 , beam supporting members  202  extending from the rear surface  198  of the mounting plate  194  and a top member  204  provided with two lugs  206  which may be used to handle the rear lifting beam  18 . 
     As illustrated in FIGS. 3,  12  and  14 , the rear lifting beam  18  consists of a bottom plate  208 , two side plates  210  and a top plate  212  all welded together so as to form a rectangular tubular beam. The bottom and the top plates  208  and  212  are one inch thick while the side plates are two inches thick. The exterior sides of the bottom and the top plates  208  and  212  are each respectively lined throughout their length with a reinforcement plate  214  having a thickness of 1½ inch. Four reinforcement plates  216  extend at right angles between the inside surface of the top  212 , the bottom  208  and the side plates  210  and are uniformly distributed along the length of the rear lifting beam  18  to improve the torsion resistance thereof. The rear lifting beam  18  is also provided with two pairs of connection plates  218  which are welded on the top plate  212  of the rear lifting beam  18  and which allow for the bolting of various types of brackets used to support the rear portion of the revolving frame F of different models of mechanical shovels. Each connection plate  218  is further supported on the underside thereof by a pair of plates  220  extending at right angles from the side plates  210  of the rear lifting beam  18 . 
     As seen in FIGS. 11 and 12, each pair of connection plates  218  allows for the bolting of an horizontal bracket  222  which is adapted to support the underside of the counterweight which is mounted to the rear of the B-E 295 BII shovel. Each horizontal bracket  222  comprises bottom and top plates  224  and  226  which have a rectangular opening  228  defined in the center thereof, the bottom and the top plates  224  and  226  being spaced apart by four spacing plates  230  mounted in a rectangular configuration around the aforementioned rectangular opening  228  and by two plates  232  extending at right angles outwardly from each spacing plate  230 . Each horizontal bracket  222  further comprises a reinforcement plate  234  extending in the center of the rectangular opening  228  and, more particularly, between the two spacing plates  230  which are transversal with respect to the rear lifting beam  18 . 
     As seen from FIGS. 13 and 14, each pair of connection plates  218  also permits for the installation of an inclined bracket  236  which is adapted to support the rear corners of the revolving frame F of the P&amp;H 2300 XPA shovel. Each inclined bracket  236  comprises first and second base plates  238  and  240  which are welded together in a staggered fashion, the base plates  238  and  240  defining a bolted pattern which allows for the bolting of a given inclined bracket  236  to a pair of connection plates  218  of the rear lifting beam  18 . Each inclined bracket  236  further comprises a pair of spaced apart inclined supports  242  which extend at right angles from the upper surface of the second base plate  240 , a rectangular plate  244  which is mounted to both inclined supports  242  so as to form an inclined supporting surface from which extends substantially at right angles an obround plate  246  having opposite semi-circular ends, the plate  246  being adapted to engage the holes defined in the rear underside of the revolving frame F′ of the P&amp;H 2300 XPA shovel so as to determine the lifting axle of the rear lifting beam  18 . Some wedges  248  must be used to fill the space between the horizontal portion of the second base plate  240  and the underside of the revolving frame F′ of the P&amp;H 2300 XPA shovel. 
     From the above, it is easily seen that the configuration of the rear lifting beam  18  allows for the installation of various types of bracket which are designed for different models of mechanical shovels. However, it is noted that some models of mechanical shovels, as for instance the P&amp;H 2100 BLE, do not require the provision of such brackets. Indeed, the P&amp;H 2100 BLE shovel is directly supported by the rear lifting beam  18 , the space between both pairs of connection plates  218  being filled up by wedges so as to offer an uniform supporting surface. Therefore, the connection plates  218  of the rear lifting beam  18  and the wedges act as a bracket; in other words, they form a support for the revolving frame F of the mechanical shovel. 
     The shovel lifting device  10  is also provided with means to determine the length stroke of each cylinder and the absolute lifting elevation of the shovel at any time during the lifting operation. These detectors are adapted to transmit their respective information to an automaton which is used to control the lifting operation. 
     More specifically, as best seen in FIGS. 2 and 3, each front and rear lifting units  12  and  14  are provided with a removable absolute lifting elevation detector assembly  250  including an absolute lifting elevation detector  254  which is mounted to the end of member  251  which extends at right angles from one of the side walls  90  and  200  of each beam connection member  82  and  180  of the front and the rear lifting beams  16  and  18 , respectively. A cable  252  is secured at one end thereof to the absolute lifting elevation detector  254  and at an opposite end thereof to a plate  256  which is anchored in the soil. The cable  252  must be perpendicular with respect to the absolute elevation detector  254  and the member  251  must be long enough to ensure that the plate  256  which is anchored in the soil will not be subjected to the packing soil effect. This allows for an accurate determination of the elevation of the revolving frame F of the mechanical shovel with respect to the soil during the lifting operation. 
     As best seen in FIGS. 5 and 7, each front and rear lifting units  12  and  14  are also provided with a removable stroke length detector assembly  258  which is mounted to a respective mounting plate  60  and  176  of its mounting box  50  and  172 , respectively. More particularly, a cable  260  is secured at one end thereof to a stroke length detector  262  and at an opposite end thereof to the base structure  48  and  156  of the front and rear cylinders  20  and  22 , respectively. The cable  260  is protected by a vertical guard  264  to prevent alteration of the position of the cable  260  during the lifting operation. The stroke length detector  262  is adapted to measure the stroke of each pair of front and rear cylinders  20  and  22  which will be greater than the absolute lifting elevation if the soil gives way under the front and the rear lifting units  12  and  14 . In order to facilitate the supervision of the lifting operation, a scale is installed on the vertical guard  264  and a pointer  266  is secured to the bottom side of the outer square casing  24  and  26  to give a visual indication of the stroke of the front and the rear cylinders  20  and  22  at any time during the lifting operation. 
     The hydraulic control unit (not shown) used in conjunction with the front and the rear lifting units  12  and  14  consists of a feed pump having a differential flow and operating at constant pressure with each pressure line thereof being provided with a flow regulator and with a directional valve. More particularly, a main line feeds a junction manifold on which the four directional valves and flow regulators are installed. Each directional valve feeds a pair of front or rear cylinders  20  and  22 , whereby the manifold is provided with two feed and two return lines for the front cylinders  20  and with two feed and two return lines for the rear cylinders  22 . The return flow passes through a filter and an oil cooler and finally returns to an oil tank. The hydraulic control unit also comprises a recirculation pump which is used to warm up the oil before the lifting operation. A spare valve is mounted in parallel fashion with each directional valve such that it can be used in the event of a failure of the valve which is normally in operation. 
     Accordingly, the fact that each front and rear lifting unit  12  and  14  is independently controlled, allows for the revolving frame F of a given mechanical shovel to be fitted and this is particularly useful during the re-engagement operation of the shaft gudgeon of the carbody C with the revolving frame F. This operation is also greatly facilitated by the automaton which has recorded the initial position of the revolving frame F of the mechanical shovel before the lifting operation and which is adapted to control all the operations. Moreover, the configuration of the hydraulic system and the joint use of the automaton which is connected to the absolute lifting elevation and stroke length detectors  254  and  262  of each front and rear lifting unit  12  and  14  ensure a uniform lifting plane, even if the front and rear lifting units  12  and  14  are not at a same level. Therefore, the present shovel lifting device  10  is adapted to maintain the initial lifting plane which is computed by the automaton before the lifting operation. Accordingly, the hydraulic control unit allows to have the same lifting speed at each front and rear lifting unit  12  and  14  during the complete lifting or lowering operation. 
     Having thus described the structure of the present invention, we will now explain the general method for lifting different models of mechanical shovels, such as the P&amp;H 2300 XPA, the P&amp;H 2100 BLE and the B-E 295 BI, 295BII. 
     First it is necessary to prepare the lifting area. More particularly, when the shovel lifting device  10  is used outside of the workshop, the operators must be sure that the ground at each front and rear lifting units  12  and  14  is substantially level. Moreover, they must check the minimal load-bearing capacity of the ground at each front and rear lifting units  12  and  14  to prevent any of these lifting units from sinking during the lifting operation of the mechanical shovel. 
     The second step consists of preparing the mechanical shovel. Having regard to the P&amp;H 2300 XPA mechanical shovel, the revolving frame F′ thereof must be turned at 180° with respect to the carbody C of the shovel to provide the space which is necessary to properly install the rear lifting beam  18  under the inclined portion at the rear of the revolving frame F′ of the P&amp;H 2300 XPA mechanical shovel. As to the P&amp;H 2100, B-E 295BI and B-E 295 BII, the revolving frames F and F″, respectively, must be at 0° with respect to the carbody C of each of these shovels. The dipper handle, the boom and the bucket of the mechanical shovel are then removed. This provides the access required for the installation of the front lifting beam  12 . 
     Once the lifting area and the mechanical shovel have been prepared, the rear lifting assembly, i.e. the rear lifting beam  18  and the associated rear lifting units  14 , can be installed. Accordingly, when required, a pair of rear brackets corresponding to the model of mechanical shovel to lift are mounted to the connection plates  218  of the rear lifting beam  18  (i.e. the inclined brackets  236  for the P&amp;H 2300 and the horizontal bracket  222  for the B-E 295II). Thereafter, the rear lifting beam  18  is put in place with respect to the revolving frame F, F′, F″ of the mechanical shovel and maintained in position by means of holders (not shown) which are temporarily installed at each end of the rear lifting beam  18 . After having so position the rear lifting beam  18 , the rear lifting units  14  are respectively disposed at opposite ends of the rear lifting beam  18  under the beam connection members  180  thereof. Each cylinder  22  of both rear lifting units  14  are then connected to the hydraulic control unit (not shown) and extended so as to align the bolting pattern of the mounting box  172  of each rear lifting unit  14  with the bolting pattern of the beam connection members  180  of the rear lifting beam  18 . Therefore, each rear lifting unit  14  is secured to the rear lifting beam  18  and the holders are removed. Thereafter, an absolute lifting elevation detector assembly  250  and a stroke length detector assembly  258  are mounted to each rear lifting unit  14 , whereby the rear reference lifting plane can be established as explained hereinbefore. 
     The fourth step consists of mounting the front lifting assembly, i.e. the front lifting beam  16  and the front lifting units  12 . As for the rear lifting beam  18 , the front lifting beam  16  is first properly positioned with respect to the mechanical shovel. More particularly, the P&amp;H 2300 XPA mechanical shovel is secured to the front lifting beam  16  by means of the pair of moveable hook assemblies  128  which extends from the front side of the front lifting beam  16 . The P&amp;H 2100 BLE is secured to the front portion of the lifting arms  118  while the B-E 295BI and 295BII mechanical shovels are secured to the rear portion of the lifting arms  118  which extend from the rear side of the front lifting beam  16 , as explained hereinbefore. Therefore, it is not always the same side of the front lifting beam  16  which faces the mechanical shovel to be lifted. It is noted that a further operation is required for the P&amp;H 2100 BLE and 2300 XPA mechanical shovels. Indeed, for these models, a spacing block  68  must be mounted on each front lifting unit  12 . As for the rear lifting beam  18 , a pair of holders (not shown) are used to temporarily support the front lifting beam  16 . After having so positioned the front lifting beam  16 , the front lifting units  12  are respectively disposed at opposite ends of the front lifting beam  16  under the beam connection members  82 . Each cylinder  20  of both front lifting units  12  are then connected to the hydraulic control unit (not shown) and extended to thus allow for the bolting of each beam connection member  82  of the front lifting beam  16  to its corresponding front lifting unit  12  so that the holders can then be removed. Accordingly, for the P&amp;H mechanical shovels, the front lifting beam  16  is secured to the spacing block  68  which is mounted on the mounting box  50  of each front lifting unit  12  while for the B-E mechanical shovels the front lifting beam  16  is directly bolted to the mounting box  50  of each front lifting unit  12 . Thereafter, as for the rear lifting assembly, an absolute lifting elevation detector assembly  250  and a stroke length detector assembly  258  are mounted to each front lifting unit  12 , whereby the front reference lifting plane can be established, as explained hereinbefore. 
     After having calibrated and recorded the lifting plane, the mechanical shovel can be lifted by operation of the front and rear cylinders  20  and  22  of the front and rear lifting units  12  and  14 . It is noted that the lifting operation can be automatically controlled by the automaton if desired. 
     It is further noted that, even though the preferred embodiment has been described with two rear lifting units  14  and two front lifting units  12 , a single rear lifting unit  14  could have been used without departing from the scope of the present invention, although two front lifting units  12  would still be used to allow for the passage of the carbody C of the mechanical shovel therebetween once the revolving frame F thereof has been raised enough and that the shaft gudgeon of the carbody C is completely disengaged from the revolving frame F. The invert configuration, i.e. one front lifting unit  12  and two rear lifting units  14  could obviously also be realized. 
     Also, it is readily understood that the lifting arms  118  can take on other configurations such as to allow the shovel lifting device  10  to lift the revolving frame of various mechanical shovels. For instance, FIGS. 15 and 16 illustrate a variant lifting arm  318  which is characterized by an upper hook  320  adapted to engage the top of the front lifting beam  16  and a lower support  322  adapted to support the revolving frame. The general configuration of the lifting arm  318  is well adapted for mechanical shovels such as the 2800XPB and the 2300XP (A+B) models. The lifting arm  318  replaces components  118 ,  120 ,  122 ,  124 ,  126 ,  132  and  140  of FIG. 4; components  120 ,  124 ,  126 ,  132 ,  136 ,  138 ,  140  and  142  of FIG. 9; and components  120 ,  124 ,  126 ,  128 ,  130 ,  132 ,  134 ,  136 ,  140 ,  146  and  148  of FIG.  10 . The lifting arm or hook  318  replaces the lifting arm  118  of FIGS. 4,  9  and  10  which is welded to the front lifting beam  16 .