Abstract:
Drive plates of a hydraulic torque wrench cartridge are thickened for extended surface contact with three pawls and a direct contact with the piston rod. The drive plates are held together and are additionally stiffened by dowel pins and shoulder screws. Snap pins are axially slide able and spring loaded connecting the piston rod with the drive plates in an easily disengage able fashion. Three pawls are arrayed in a pitch adjusted with respect to the ratchet teeth pitch in correspondence with an elastic deformation of the drive plates for a balanced force transfer across them. The pawl-tooth interfaces are also in an outward opening angle preventing them from snapping free under load.

Description:
CROSS REFERENCE 
     The present application cross references the concurrently filed U.S. patent application of the same Inventor titled “Hydraulic Torque Wrench with Automatic Hold Pawl” Ser. No. 14/258,400, which is hereby incorporated by reference. 
     FIELD OF INVENTION 
     The present invention relates to hydraulic torque wrenches utilizing a ratchet cartridge. 
     BACKGROUND OF INVENTION 
     Hydraulic torque wrenches are well known power tools for tightening and loosening nuts and bolts. A hydraulic pump commonly pressurizes a hydraulic fluid that is circulated to and from the hydraulic torque wrench via hoses. The hydraulic torque wrench itself commonly features a piston that transforms the fluid pressure into a piston force, which in turn is transferred via a piston rod onto drive plates, and via one or two pawls onto a ratchet wheel that is sandwiched between the drive plates. The ratchet wheel commonly connects to a nut or itself has an internal cutout that matches the nut or bolt head to be tightened or loosened. 
     Since nuts and bolts are commonly tightly assembled, it is desirable to have a hydraulic torque wrench as compact as possible while at the same time providing a maximum torque and reliable and lasting functionality. The weakest link in the force transmission path from the hydraulic piston to the ratchet wheel is/are commonly the pawl(s) that has/have to reliably engage with a corresponding tooth of the ratchet wheel. Ratchet wheel and pawl(s) are assembled in a cartridge between two lateral plates as is well known in the art. During return travel of the hydraulic piston, the pawl(s) has/have to disengage with the ratchet wheel. Since the pawl(s) is/are much closer positioned to the torque transfer axis than the commonly more peripheral piston rod—drive plate interface, the actual force transmitted across the pawl(s) is in accordance with the well known lever principle substantially higher than the actually produced piston force. Excessive wear commonly occurs in the plate-pawl and pawl-tooth interfaces. Therefore, there exists a need for improved plate-pawl and pawl-tooth interfaces. The present invention addresses this need. 
     Two cartridge pawls have been employed in the prior art to divide the force to be transmitted onto the ratchet wheel. Nevertheless, it has been discovered by the Applicant that deformation during power strokes causes displacement of the pawls resulting in uneven loads and contact pressures. The present invention addresses this discovery for balanced load and contact pressures in all plate-pawl and pawl-tooth interfaces providing for up to three cartridge pawls to be employed simultaneously. 
     Ratchet cartridges need to be conveniently replaced especially in cases where the ratchet wheel itself connects to the nut and/or bolt head to be tightened and loosened. Nevertheless, in the prior art commonly the piston rod had to be taken apart in order to remove the ratchet cartridge from the overall torque wrench housing. Therefore, there exists a need for a simple and reliable connection between ratchet cartridge and piston rod that can be fast and easily disconnected and reconnected. The present invention addresses also this need. 
     SUMMARY 
     A ratchet cartridge features drive plates that have castles extending within the width of the ratchet wheel. The drive plates are held together and are additionally stiffened by dowel pins and shoulder screws. The castles provide for plate-pawl interfaces that extend across the entire width of the cartridge pawls, which substantially reduces contact pressures and affiliated wear in the plate-pawl interfaces. 
     The rod-plate interface is includes a rod push face at the distal end of the piston rod pushing directly onto a rod receive face within the drive plate castles. The region around the rod-plate interface axis is thereby freed from direct piston push force transfer. Instead, axially slide able and spring loaded snap pins are employed that engage with corresponding pin receive holes in the drive plates. Release access holes peripherally connect with the pin receive hole for a convenient disengaging of the snap pins and separation of the ratchet cartridge. To reassembly the ratchet cartridge, the snap pins are automatically depressed by pin actuation chamfers while the ratchet cartridge is moved into assembly position. The snap pins snap in as soon as the rod-plate interface comes into mating contact. 
     Preferably three cartridge pawls are employed and the load transfer between them is balanced out by adjusting the pitch of their plate-pawl interfaces around the torque transfer axis in correspondence with the load deformation of the drive plates, ratchet wheel and cartridge pawls. 
     A reliable and balanced contact pressure distribution in the pawl-tooth interfaces is achieved by defining a contact angle between the cartridge pawl front faces and the ratchet tooth flanks of the pawl-tooth interfaces such that a gap between the cartridge pawl end face and the ratchet tooth flank increases in direction away from the torque transfer axis while the cartridge pawl end faces are in a load free contact with their mating ratchet tooth flanks. As a result, contact pressures ramp up in the pawl-tooth interfaces starting from closest to the torque transfer axis and peak pressures are kept in the grooves of the ratchet teeth. At the same time a resulting torque on the pawls causes them to be pushed into the ratchet teeth grooves, which effectively prevents inadvertent snapping free of the cartridge pawls under load. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a side view of a hydraulic torque wrench of the present invention. 
         FIG. 2  is a front view of the hydraulic torque wrench of  FIG. 1 , with a cover shroud removed for visual access to the ratchet cartridge. 
         FIG. 3  is a first spatially angled view onto the hydraulic torque wrench of  FIG. 2 . 
         FIG. 4  is the first spatially angled view of the ratchet cartridge and a hydraulic piston assembly of  FIG. 3 . 
         FIG. 5  depicts the content of  FIG. 4  without one frontal drive plate. 
         FIG. 6  depicts the content of  FIG. 4  cut along a vertical plane. 
         FIG. 7  is a second spatially angled view onto the drive plate and the cut piston and piston rod of  FIG. 6 . 
         FIG. 8  is a side view of the content of  FIG. 6 . 
         FIG. 8A  is a detail view of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1, 2, 3, 4 , a hydraulic torque wrench  101  has a hydraulic piston  305  that is transforming a hydraulic pressure into a piston force along a piston axis  109 A. The pressurized fluid is preferably communicated to and from hydraulic torque wrench  101  via a hose connect swivel  113  peripherally connected to a housing  105 . The housing  105  has a cartridge housing  108  with a cartridge cavity  107  that encapsulates a ratchet cartridge  201  and a piston housing  109  that encapsulates a piston assembly  301  including the hydraulic piston  305  and a piston sleeve  308 . An attachment flange  118  is preferably around a torque transfer axis  123 A at a distal end of the cartridge housing  108 . A torque transfer feature  123  is rotate able around the torque transfer axis  123 A and may be an external feature extending outside the cartridge housing  108  such as a square stud as shown in the  FIGS. 1-3 . The torque transfer feature  123  may also be an internal feature residing inside the cartridge housing  108  as is well known in the art. 
     As shown also in  FIGS. 5, 6, 8 , a piston rod  312  is in contact with the hydraulic piston  305  and is receiving the piston force from the hydraulic piston  305 . The piston rod  312  has a rod rear  313  that is mating the hydraulic piston at its end and a rod head  314  that has at its end a rod push face  322  and a rod retention hole  313 . The rod push face  322  is corresponding to a rod receive face  228  of drive plates  208  that sandwich and partially encompass a ratchet wheel  203 . Drive plates  208  and ratchet wheel  203  are part of the ratchet cartridge  201 . The rod retention hole  313  is corresponding to snap pin receive holes  216  preferably in both drive plates  208 . The rod push face  322 , rod receive face  228 , rod retention holes  316  and snap pin receive holes  216  are part of a rod-plate interface and are preferably concentric with respect to rod-plate interface axis  208 A. The drive plates  208  receive the piston force from the piston rod  312  via the rod-plate interface. 
     Due to the snap connection between the piston rod  312  and the ratchet cartridge  201 , the rod rear  313  and the rod head  314  may be pre assembled through the piston sleeve  308  prior to attachment of the piston sleeve  308  with the hydraulic piston  305 . In  FIG. 6 , the rod rear  313  is shown in uncut view with its spherical rod rear head  318  and a tightening crown  319  with preferred contour of a hex that is radially recessed into the spherical rear head  318 . Via the tightening crown  319  the rod rear  313  may be conveniently screwed into and combined with the rod head  314  through the piston sleeve  308 . This provides for a rod combine interface between the rod rear  313  and the rod head  314  that does not need to be structurally compromised to accommodate for radial tightening flats as they are well known in the prior art. As a favorable result, the rod combine interface has improved structural strength to transfer the piston force while reducing the risk of buckling. The tightening crown  319  in turn fits in between the piston/rod interface and the rod/sleeve interface without compromising their contact areas. 
     Part of the ratchet cartridge  201  are also preferably three cartridge pawls  232  that receive the piston force from the drive plates  208  via respective plate-pawl interfaces. The cartridge pawls  232  preferably each feature a cartridge pawl wing  238  and a cartridge pawl shaft  236  that sticks out on both ends. The cartridge pawl wing  238  has a spring blind hole  235 . On its distal end it has a cartridge pawl front face  240  and a pawl front edge radius  239 . Cartridge pawl springs  234  may be contained in the spring blind holes  235  and push the cartridge pawl wings  238  towards the ratchet wheel  203 . Part of each plate-pawl interface is a pawl shaft mating face  237  provided by the drive plates  208  and the cartridge pawl shaft  236 . Pawl shaft mating faces  237  and cartridge pawl shafts  236  are concentric with respective plate-pawl interface axes  237 A. 
     The ratchet wheel  203  is rotate able held in the cartridge housing  108  and rotate able held on to by the drive plates  208  concentric with respect to the torque transfer axis  123 A. The ratchet wheel  203  is receiving the piston force from the cartridge pawls  232  via a pawl-tooth interface such that the piston force is transformed into a torque around the torque transfer axis  123 A. Part of each pawl-tooth interface is a respective pawl front face  240  and pawl front edge radius  239  on the side of the cartridge pawls  232  and a respective one of a number of ratchet tooth flanks  205  and tooth base radii  207  on the side of the ratchet wheel  203 . Ratchet tooth flanks  205  and tooth base radii  207  are arrayed around the circumference of the ratchet wheel  203  in a ratchet teeth pitch  205 P. Respective pawl front edge radii  239  and tooth base radii  207  are defining pawl-tooth interface axes  207 A through which a cartridge force vector  232 V passes at the moment the piston force starts to ramp up. 
     During initial piston force transfer and before elastic deformation occurs in the drive plates  208 , the ratchet wheel  203  and the cartridge pawls  232 , contact in the pawl-tooth interfaces is substantially only between the respective tooth base radii  207  and pawl front edge radii  239 . Consequently and as is clear to anyone skilled in the art, each respective initial force vector  232 VI is angularly defined by the position of the respective plate-pawl interface axis  237 A and pawl-tooth interface axis  207 A within the ratchet cartridge  201  as shown in  FIG. 8A . At the same time and while the plate-pawl interfaces are in a substantially load free mating contact, the cartridge pawl front faces  240  and respective ratchet tooth flanks  205  are in a pawl clearance angle  240 C such that a gap between them increases in direction away from the torque transfer axis  123 A. The initial force vector  232 VI is in an initial vector angle  232 AI to the respective tooth flank  205  within the ratchet cartridge  201  and within a mating pawl-tooth interface that is substantially less than ninety degrees. Consequently, as the piston force starts, initial piston force transfer in the pawl-tooth interface is across the pawl front edge radii and respective tooth base radii  207  only. Due to the off perpendicular initial vector angle  232 AI a resulting initial torque forces the respective cartridge pawl  232  towards the ratchet wheel  203  as is clear to anyone skilled in the art. As the piston force ramps up, deformations occur in drive plates  208 , ratchet wheel  203  and cartridge pawls  232  that cause the clearance angle  240 C to decrease and contact pressure to extend more and more into the ratchet tooth flanks  205  and pawl front faces  240 . The clearance angle  240 C is selected in conjunction with the deformation behavior of drive plates  208 , ratchet wheel  203  and cartridge pawls  232  and a predetermined maximum of the piston force such that only at the predetermined maximum piston force, contact pressures in the pawl-tooth interfaces reach the circumferential end of the ratchet teeth  205 . In that way, the risk of snapping free of the cartridge pawls  232  under peak load due to wear in the pawl-tooth interface is substantially eliminated. In addition, the position of the plate-pawl interface axes  237 A within the ratchet cartridge assembly  201  and the tooth angle  205 A of the ratchet tooth flanks  205  with respect to the torque transfer axis  123 A are selected such that the peak vector angle  232 AP remains below ninety degrees. As a result, even during peak piston force transfer, there remains a torque that forces the cartridge pawls  232  towards the ratchet wheel  203 . This also effectively opposes inadvertent snapping free of the cartridge pawls  232  during peak piston force transfer. The clearance angle  240 C is preferable between 0.5 and 5 degrees. 
     Preferably both drive plates  208  feature a drive plate base  209  that extends lateral to the ratchet wheel  203  and a drive plate castle  210  that extends within the width of the ratchet wheel  203 . The drive plate castles  210  of both drive plates  208  are preferably in direct contact along respective plate mating faces  227  while each of the two drive plates  208  is assembled on one of the two lateral sides of the ratchet wheel  203 . The drive plates  208  are connected with dowel pins  243  and a drive plate tensioner  219  such as a well known shoulder screw. The dowel pins  243  and drive plate tensioner  219  extend radially tight within dowel pin holes  244  and tensioner hole  220  through the drive plate castes  210  up to the plate mating faces  227 . The radial tight fit up to the plate mating faces  227  provides accurate positioning of the two drive plates  208  with respect to each other within the ratchet cartridge  201  and increases bending stiffness of the two drive plates  208  as is clear to anyone skilled in the art. The stiffened drive plate castles  210  provide for balanced contact pressures in the rod-plate and plate-pawl interfaces that preferably extend within the drive plate castles  210 . 
     The rod-plate interface with its rod push face  322  and a rod receive face  228  is snug contacting the rod push face  322  while the rod-plate interface is in mating contact. As a favorable result, the piston force is directly transferred from the piston rod  312  onto the drive plates  208  across a substantially larger interface area than in prior art pin style rod-plate push force transferring interfaces. This reduces contact pressures and reduces wear. At the same time it gives room for a snap mechanism in the central area around the rod-plate interface axis  208 A around which the piston rod  312  is rotate able with respect to the drive plates  208  while the rod-plate interface is in mating contact. The snap mechanism includes preferably two rod snap pins  218  that are axially with respect to the rod-plate interface axis  208 A slide able and spring loaded via a snap pin spring  217  within the rod retention hole  316 . While the rod-plate interface is in mating contact, the rod retention hole  316  is axially aligned with the snap pin receive holes  216  to axially receive the rod snap pins  218  and lock the rod-plate interface rotate able. The rod-plate interface axis  208 A is perpendicular to the piston axis  109 A. 
     Release accesses  213  provide peripheral access across the drive plates  208  to the snap pin receive holes  216 . As a result, the snapped in pins  218  may be conveniently peripherally disengaged from the snap pin receive holes  216  via the release accesses  213 . The release accesses  213  are preferably blind holes extending approximately perpendicular to the snap pin receive hole  216  across the drive plates  208  for accessing the rod snap pins  218  across the drive plates  208  in a direction substantially aligned with the piston axis  109 A. That way, the ratchet cartridge  201  is accessed for disengaging from the piston rod  312  by removing only a well known housing shroud from the cartridge housing  108  as is depicted in  FIGS. 2, 3 . This greatly simplifies replacement of the ratchet cartridge  201  compared to the prior art. To reconnect the ratchet cartridge  201  with the piston rod  312  within the otherwise assembled hydraulic torque wrench  101 , the ratchet cartridge  201  merely needs to be pushed with its rod clearance cutout  229  towards the rod head  314 . As the clearance cutout  229  slips over the rod head  314 , the laterally extending rod snap pins  218  are depressed against the snap pin spring  217  by the pin actuation chamfers  214  along the peripheral edges of the rod clearance cutout  229 . 
     The cartridge pawls  232  are arrayed with their respective plate-pawl interfaces around the torque transfer axis  123 A in front pawl pitch  237 F and rear pawl pitch  237 R that differ from the ratchet teeth pitch  205 P by a pitch difference such that the piston force is evenly transferred across the cartridge pawls  232  in conjunction with the piston force related deformation of the drive plates  208 , the ratchet wheel  203  and the cartridge pawls  232 . In the preferred embodiment with three employed cartridge pawls  232 , the pitch difference may be +/−0.02-1% of the ratchet teeth pitch  205 P such that the front pawl pitch  237 F is smaller and the rear pawl pitch  237 R is larger than the ratchet teeth pitch  205 P. Consequently, at the begin of a power stroke when the piston force ramps up from zero while the cartridge pawls  232  are engaged, initially only the middle cartridge pawl  232  transfers the piston force. As the piston force increases and elastic deformation occurs in the drive plates  208 , the ratchet wheel  203  and the cartridge pawls  232 , front and rear pawl  232  begin to transfer a portion of the piston force as well. As the piston force and deformation peaks, the piston force is evenly balanced out across all three cartridge pawls  232 . 
     The piston forces cause bending stresses in the studs of the pawl shafts  236  and substantial stress concentrations in the transition corners between the cartridge pawl wings  238  and the shaft studs extending beyond the cartridge pawl wings  238 . A pawl shaft transition radius  246  placed there substantially evens out such stress concentrations. To provide room for these pawl shaft transition radii  246 , pawl shaft corner clearances  247  may be recessed into the drive plate bases  209  as shown in  FIG. 7 . 
     The drive plates  208  are rotate able holding on to ratchet wheel flanges  225  on both lateral ends of the ratchet wheel  203  via ratchet wheel bushings and ratchet side mating faces  226  as is well known in the art. The ratchet wheel  203  has an internal torque transfer spline  221 . In the depicted embodiment with an external torque transfer feature  123  such as a well known square end shaft, the torque transfer spline  221  is engaging with a mating spline of the shaft, which in turn is rotate able held in the cartridge housing  105  as is well known in the art. In an alternate configuration of the claimed hydraulic torque wrench  101  and ratchet cartridge  201  for limited clearance applications, the torque transfer spline  221  may be configured and shaped to mate directly with a nut and/or bolt to be tightened and/or loosened. In that case, the lateral ratchet wheel flanges  225  may axially extend beyond the drive plates  208  for a direct rotate able hold within the attachment flanges  118 . 
     To operate the hydraulic torque wrench  101 , it may be connected via the hose connect swivel  113  to well known hydraulic feed and return hoses via which pressurized hydraulic fluid may be communicated to and from the hydraulic piston  305 . Upon build up of fluid pressure, the resulting piston force acting on the ratchet cartridge  201  causes the drive plates  208  to rotate around the torque transfer axis  123 A. During such power stroke, the cartridge pawls  232  are engaged with ratchet teeth flanks  205  such that the piston force and rotational movement of the drive plates  208  is transferred onto the ratchet wheel  203  and torque is exerted via the torque transfer feature  123 . Once the hydraulic piston  305  has reached its travel end it stalls and fluid flow in the hoses needs to be reversed to return the piston back to its most rearward position. During return travel, the snap mechanism returns the drive plates  208  with its disengaged cartridge pawls  232 . The ratchet wheel remains in position until the ratchet cartridge  201  is in its most rearward position and the cartridge pawls  232  engage in the next following set of ratchet teeth flanks  205  and the next power stroke is ready to start. In the preferred embodiment of the invention, pawl pitches  237 R and  237 F are selected such that each of the preferably three cartridge pawls  232  engage with a single ratchet tooth flank  205  to take advantage of the features and their functionality as described in conjunction with  FIG. 8 . 
     The compact sizing of the ratchet cartridge  201  provides for increased spacing within the cartridge cavity  107  to accommodate for an automatic hold pawl actuation system as is taught in the cross references application. 
     Accordingly, the scope of the present invention as described in the above and the Figures is set forth by the following claims and their legal equivalent: