Patent Publication Number: US-2015083540-A1

Title: Dog clutch having fluid pressure activated sliding internal gear

Description:
PRIOR APPLICATION 
     This application claims the benefit of U.S. Provisional Application Ser. No. 61/641,280 filed 2012 May 1. 
    
    
     FIELD OF THE INVENTION 
     The instant invention relates to mechanical clutch assemblies and more particularly to dog clutch assemblies adapted to disengagingly connect to a motor drive shaft. 
     BACKGROUND 
     Mechanical clutches of various types temporarily couple power from a power source such as the rotating shaft of a motor to a shaft-driven auxiliary load device such as an hydraulic pump. The clutch allows power to be transmitted from the power supply shaft to the load shaft when the clutch is engaged and allows the power supply shaft to rotate essentially unimpeded when the clutch is disengaged. 
     As with many mechanical components it is often preferred that it be rugged, and inexpensive to manufacture, assemble, operate, maintain and repair. In particular to clutches, it is often preferred that friction on the power drive shaft is minimized when the clutch is disengaged. In particular to power takeoff clutch devices maintaining a compact assembly can help reduce bulk on a commercial vehicle. 
     Another type of clutch is a geared clutch also known as a dog clutch which uses a sliding gear to connect and disconnect the powered, drive shaft to the load shaft. The dog clutch disclosed in Robinson, U.S. Pat. No. 7,832,538 incorporated herein by reference, (hereinafter “Robinson”) is used to disengagingly drive an hydraulic pump in a commercial vehicle using a power takeoff (PTO) from the vehicle&#39;s main motor. 
     The Robinson device presents some problems in practice. First, the sliding shift fork can introduce off-axis forces which can lead to greater wear and jamming of the clutch or sliding gear. Second, the sliding gear contacts the fork directly leading to greater wear. Third, the use of the lock teeth can wear against the spline ends of the drive and load shafts. 
     The instant invention results from efforts to improve dog clutches. 
     SUMMARY 
     The primary and secondary objects of the invention are to provide an improved dog clutch. These and other objects are achieved in a first aspect by providing a roller bearing supported internally toothed annular power transmitting collar gear which can reciprocatingly slide coaxially to engage and disengage a driving shaft from a load shaft. In some embodiments the temporarily engaged shaft and collar gear have cooperative teeth in which there is a first set of teeth having a given axial length and a second interleaved set having a shorter length. 
     In some embodiments there is provided that in a dog clutch assembly, comprising: a first shaft having an interface end portion with teeth on its outer diameter, the first shaft having a longitudinal axis; a second shaft having an interface end portion with teeth on its outer diameter, the second shaft having a longitudinal axis that is collinear with the longitudinal axis of the first shaft; a gap between the first shaft and the second shaft in a direction along the longitudinal axes of the shafts; an annular clutch having teeth along its inner diameter that engage the teeth of the first shaft and teeth of the second shaft when the clutch is in an engaged position, and that engage only the teeth of the first shaft or the teeth of the second shaft when it is in a disengaged position, wherein the engaged position and the disengaged position are linearly displaced from one another along the longitudinal axis of the shafts; an improvement wherein said annular clutch comprises: a first subset of said annular clutch teeth having a first length; and; a second subset of said annular clutch teeth having a second length shorter than said first set. 
     In some embodiments the improvement further comprises: a driving actuator that drives the clutch between the engaged position and the disengaged position; wherein said driving actuator comprises: a first annular piston in direct contact with a second annular piston slidingly connected to said clutch. 
     In some embodiments said driving actuator further comprises: a first portion of said first piston residing in a first pressure-based chamber; a second portion of said second piston residing in a second pressure-based chamber; wherein the presence of fluid under sufficient pressure in one of said portions actuates the clutch. 
     In some embodiments said first shaft is rotatively supported by said second shaft by a pilot bearing. 
     In some embodiments the improvement further comprises a wave spring resisting axial movement of said pilot bearing. 
     In some embodiments the improvement further comprises: said first and second shafts comprise ferrous metal; a plural number of permanent magnets balancingly fitted to at least one of said shafts in locations exposed to wear fragments generated by the engaging and disengaging teeth during operation of said annular clutch assembly. 
     In some embodiments there is provided that in a dog clutch assembly, comprising: a first shaft having an interface end portion with teeth on its outer diameter, the first shaft having a longitudinal axis; a second shaft having an interface end portion with teeth on its outer diameter, the second shaft having a longitudinal axis that is collinear with the longitudinal axis of the first shaft; a gap between the first shaft and the second shaft in a direction along the longitudinal axes of the shafts; an annular clutch having teeth along its inner diameter that engage the teeth of the first shaft and teeth of the second shaft when the clutch is in an engaged position, and that engage only the teeth of the first shaft or the teeth of the second shaft when it is in a disengaged position, wherein the engaged position and the disengaged position are linearly displaced from one another along the longitudinal axis of the shafts; an improvement which comprises: a driving actuator that drives the clutch between the engaged position and the disengaged position; wherein said driving actuator comprises: a first annular piston in direct contact with a second annular piston is rotatively connected to said clutch. 
     In some embodiments the driving actuator further comprises: a first portion of said first piston residing in a first pressure-based chamber; a second portion of said second piston residing in a second pressure-based chamber; wherein the presence of fluid under sufficient pressure in one of said portions actuates the clutch. 
     In some embodiments the presence of fluid under sufficient pressure in said first portion drives said clutch toward said engaged position and wherein the presence of fluid under sufficient pressure in said second portion drives said clutch toward said disengaged position. 
     In some embodiments the improvement further comprises a stop surface of said second piston contacts a stop surface in said second chamber when said clutch is in said engaged position; and wherein a stop surface of said first piston contacts a stop surface in said first chamber when said clutch is in said dis-engaged position. 
     In some embodiments said first piston rotatively connects to said clutch through a first clutch bearing; and wherein said second piston rotatively connects to said clutch through a second clutch bearing; and wherein said direct contact limits axial loads on said clutch bearings. 
     In some embodiments the improvement further comprises: a first subset of said annular clutch teeth having a first length; and; a second subset of said annular clutch teeth having a second length shorter than said first set. 
     In some embodiments said first shaft is rotatively supported by said second shaft by a pilot bearing. 
     In some embodiments the improvement further comprises a wave spring resisting axial movement of said pilot bearing. 
     In some embodiments the improvement further comprises: said first and second shafts comprise ferrous metal; a plural number of permanent magnets balancingly fitted to at least one of said shafts in locations exposed to wear fragments generated by the engaging and disengaging teeth during operation of said annular clutch assembly. 
     The content of the original claims is incorporated herein by reference as summarizing features in one or more exemplary embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatical perspective illustration of an assembled dog clutch assembly according to an exemplary embodiment of the invention. 
         FIG. 2  is a diagrammatical side plan view illustration of the assembled dog clutch assembly of  FIG. 1 . 
         FIG. 3  is a diagrammatical front plan view illustration of the assembled dog clutch assembly of  FIG. 1 . 
         FIG. 4  is a diagrammatical perspective exploded illustration of a dog clutch assembly of  FIG. 1 . 
         FIG. 5  is a diagrammatical perspective exploded illustration of some of the major components of a dog clutch assembly of  FIG. 1 . 
         FIG. 6  is a diagrammatic cross-sectional side view of the dog clutch assembly of  FIG. 1  taken along line  6 - 6  of  FIG. 3  in the engaged position. 
         FIG. 7  is a diagrammatic cross-sectional side view of the dog clutch assembly of  FIG. 1  taken along line  6 - 6  of  FIG. 3  in the disengaged position. 
         FIG. 8  is a diagrammatic cross-sectional side view of the temporarily engaged shaft and collar gear having bifurcated teeth lengths in the act of being engaged. 
         FIG. 9  is a diagrammatic cross-sectional side view of the temporarily engaged shaft and collar gear in the power transmitting condition. 
         FIG. 10  is a diagrammatic cross-sectional side view of the temporarily engaged shaft and collar gear in the power transmitting condition using both sets of bifurcated length teeth. 
         FIG. 11  is a diagrammatical perspective exploded illustration of a dog clutch assembly according to an alternate exemplary embodiment of the invention. 
         FIG. 12  is a diagrammatical perspective exploded illustration of the drive shaft portion of the assembly of  FIG. 11 . 
         FIG. 13  is a diagrammatical perspective exploded illustration of the load shaft portion of the assembly of  FIG. 11 . 
         FIG. 14  is a diagrammatical perspective exploded illustration of the rearward piston and inter-piston guide pins of the assembly of  FIG. 11 . 
     
    
    
     DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     Referring now to the drawing, there is illustrated in  FIGS. 1-7  a dog clutch assembly  1  according to an exemplary embodiment of the invention. 
     The assembly  1  includes a housing  2  having an internal cavity  3  for containing most of the other components of the clutch assembly. The housing has a front flange  4  adapted to secure the housing to a substantially stationary structure associated with a power supplying shaft (not shown) such as a power takeoff (PTO) and a back flange  5  adapted to secure the housing to a substantially stationary structure associated with a shaft driven load unit such as an hydraulic pump. The front flange surrounds the clutch assembly&#39;s rotatively supported drive shaft  6  which connects to the power supplying shaft. A bearing  7  rotatively supports the drive shaft with respect to the front flange. Another bearing  8  rotatively supports the load shaft  9  with respect to the back flange  5 . The back flange surrounds the clutch assembly&#39;s rotatively supported load shaft which connects to the shaft of the load unit. When assembled, the flanges are separated by a substantially cylindrical housing side wall  10 . The drive shaft and load shaft are located coaxially along a common rotation axis  11 . 
     Axial movement of the two shafts with respect to the housing is restricted by a pair of snap rings  20 . The temporarily engaged drive shaft can be formed by an outwardly extending shaft  21  coupled with a continuously engaged ring gear  22 . The ring gear and extending shaft can be engaged by cooperative splines as shown or other keyed mechanisms which angularly couple the extending shaft to the ring gear. The ring gear thus becomes the element of the assembly which is temporarily engaged by the collar gear. Thus, the combined extending shaft and ring gear can be referred to collectively as the temporarily engaged shaft, or in this embodiment, the drive shaft. A snap ring  23  restricts relative axial movement between the ring gear and extending shaft. 
     Threaded lubrication holes  25  are sealed by removable threaded plugs  26 . A central friction fitting plug  27  seals the central lumen  28  of the load shaft. Seals  29  seal the junction between the shafts and the housing. A pair of drive fluid intake ports  31 , 32  penetrate through the housing wall to supply air or other fluid for activating the clutch. 
     The facing ends  34 , 35  of the shafts internal to the assembly housing are coaxial and splined to have outwardly projecting teeth  36 , 37 . The shafts are axially spaced apart by an axial distance to form a gap  40  therebetween. 
     Power is transmitted from the drive shaft to the load shaft by a coaxial internally toothed collar gear  41  also known as a slider gear, also known as an annular clutch, which can reciprocatingly slide coaxially to engage and disengage a driving shaft from a load shaft. The collar gear can have inwardly projecting teeth  42  shaped dimensioned and oriented for engaging the two shafts. The collar gear engages both shafts during power transmitting operation when the collar gear is in the engaged position. Power is disconnected between the shafts when the collar gear slides axially off the drive shaft but remains on the load shaft when the clutch is in the disengaged position. Although in this embodiment the drive shaft is the temporarily engaged shaft and the load shaft is the continuously, or non-temporarily engaged shaft, the two could be switched so that the load shaft is temporarily engaged and the drive shaft is continuously engaged. 
     As shown primarily in  FIGS. 6-7 , the axial movement of the collar gear between the engaged and disengaged position is controlled by a pneumatically driven system acting on a pair of coaxial annular pistons  51 , 52  rotatively coupled to the collar gear by a pair of coaxial rolling-element bearings  53 , 54 . The pistons move axially within a pair of coaxial annular chambers  55 , 56  formed by a pair of coaxial annular piston housings  57 , 58  located astride the axial range of movement of the pistons. By providing roller-element bearings, there is less wear on the collar gear and the actuation elements including the pistons. Sealer rings  60  form substantially hermetic seals between the pistons and their respective piston housings and between the piston housings and the assembly housing. Guide pins  61  restrict angular movement of the pistons with respect to the housings while allowing axial movement. Angular and cooperatively engaging crenelations  62  are formed on the abutting surfaces  63  of the pistons so that their mutual angular orientation is assured. 
     As shown in  FIG. 6 , in order for the assembly to be in the engaged position, air is injected into the port  32  in fluid communication with one of the chambers  56  formed between the piston  52  and the piston housing  58 , which forces the piston to move axially out of the chamber, driving the collar gear  41  over the end of the drive shaft, and consequently driving the other piston  51  into its associated piston housing  57  and engaging the other chamber  55 . 
     As shown in  FIG. 7 , in order for the assembly to be in the disengaged position, air is injected into the port  31  in fluid communication with the other chamber  55  formed between the piston  51  axially nearer to the drive shaft and its piston housing  57 , which forces that piston to move axially out of its chamber, driving the collar gear  41  off the end of the drive shaft and completely onto the load shaft, and consequently driving the piston  52  nearest the load shaft into its associated piston housing  58  and engaging its chamber  56 . 
     A number of arcuately oval depressions  65  can be formed into the faces  66  of the pistons facing their respective chambers so that guide pins can engage them and restrict angular rotation of the pistons with respect to their piston housings and so that air can initially more easily begin to flow into the chamber when the piston is fully engaged in its respective piston housing. The arcuate oval shape can be used to provide for slight angular play to facilitate assembly. 
     Although pneumatic actuation is used in the exemplary embodiment, the assembly can be adapted to use other driving fluids such as hydraulic fluid. In addition, the assembly can be adapted so that movement of the slider gear can be accomplished using other mechanical or electro-mechanical means known in the art. 
     As shown in  FIG. 8  the temporarily engaged shaft  70  and collar gear  71  are formed to have cooperative sets of teeth  72 , 73  having bifurcated axial lengths. Specifically, a first set of teeth  72  are formed having a first longer axial length L 1 . A second set of teeth  73  shorter axial length L 2  are interspersed between the longer teeth so that every other tooth is a member of one of the sets. 
     As shown in  FIG. 8 , during an engagement action the slider gear slides over the temporarily-engaged gear so that the ends  74  of the longer teeth pass into the spacing  75  formed between the longer teeth of the gear and shaft. Relative angular motion between the slider gear and the temporarily-engaged gear typically occurs during the engagement action until the faces  76 , 77  of the teeth bear against one another as shown in  FIG. 9  so that torque and be transmitted. The collar gear can continue to slide axially in alignment until the collar gear has fully engaged the temporarily-engaged gear to be in the engaged position. 
     The bifurcated length teeth provide several advantages over a slider gear and temporarily-engaged gear having a single set of enmeshing teeth. 
     First, during an engagement action there is a lesser chance that the axial travel of the slider gear is temporarily blocked from engagement due to a non-synchronization with the temporarily-engaged gear. In other words, if the relative angular orientation of the two gears is such that the leading ends of the teeth of the slider gear contact the leading ends of the teeth on the temporarily-engaged gear, there may be a delay in full engagement or increased wear on the teeth ends. By creating more unblocked angular space for the gears ends to mesh the chances of the teeth being in a blocking orientation during an engagement action are reduced 
     Second, since the opposite end of the slider gear has essentially a standard spline it can engage the always-engaged gear using both sets of teeth to restrict that interface from relative angular motion. In other words, the greater spaced apart longer teeth are fully capable of engaging every other tooth of the spline of the continuously engaged gear. 
     The shorter length teeth are easily manufacture by first creating a single set of longer teeth. Then every other one of the longer teeth is machined to remove material and make the selected every-other tooth shorter. 
     For many applications such as the power takeoff disconnect for hydraulic pumps on commercial vehicles, where backlash between the slider gear and temporarily-engaged gear is not a problem, only the longer axial length teeth set between the two gears need be engaged. However, in other applications where backlash is to be avoided, the axial length of the shorter set of teeth can be made longer so that in a full engagement position as shown in  FIG. 10  both sets of teeth are engaged between the slider gear and the temporarily-engaged gear, restricting relative angular motion between the gears and essentially eliminating any offending backlash. 
     It has been found that the bifuracted axial length teeth, in which there is a first set of teeth having a given axial length and a second interleaved set having a shorter length, also provide improved engagement action by better lubrication because the presence of the shorter teeth within the spacing of the longer teeth helps carry a miniscus of lubrication fluid nearer to the ends of the longer teeth. In other words, through surface tension forces it has been found that the presence of the shorter teeth help provide more lubrication to the ends of the longer teeth than would be expected if only double-spaced, longer teeth were used. 
     Because the collar gear is sandwiched between a pair of abutting ring-shaped pistons the pistons protect the collar ring and bearings against contacts and greater axial loads during the engage and disengage actions especially when the piston reach the end of their ranges of motion. In other words, when a piston is forced into position it can strike against the wall of its housing accommodating the load of the axial motion rather than the collar gear or the bearings. The combination of the piston and housing creates a stop surface to prevent over-travel of the sliding gear. This reduces the stresses on the collar gear and bearings allowing for greater life of the part and potentially reduced bulkiness of the parts. 
     Such a dog clutch mechanism is particularly suited to disengagingly couple a power takeoff (PTO) to an hydraulic pump on a commercial vehicle such as a waste disposal truck. 
     In this specification the piston in contact with the pressurized fluid can be known as the pressurized piston and the other piston which is retracting into its “housing” can be known as the non-pressurized piston. 
     By providing the separated pair of roller bearings between the sliding collar gear and the pistons additional bearing support is provided continuously to the load shaft and intermittently to the drive shaft. Both shafts are engaged during power transmission in the engaged position. In this way the size of the assembly can be further reduced. 
     Referring now to  FIGS. 11-14  there is shown a dog clutch assembly  101  according to an alternate exemplary embodiment of the invention. This embodiment operates similarly to the embodiment of  FIG. 1  except where indicated below. 
     The assembly  101  includes a housing  102  having a front flange  104 , and a back flange  105 . A bearing  107  rotatively supports a drive shaft  106  with respect to the front flange and is secured to the housing by a snap ring  184 . Another bearing  108  rotatively supports the load shaft  109  with respect to the back flange  105 . When assembled the flanges are separated by a substantially cylindrical housing side wall  110 . The drive shaft and load shaft are located coaxially along a common rotation axis  111 . 
     Axial movement of the two shafts with respect to the housing is restricted by a pair of snap rings  120 . The temporarily engaged drive shaft can be formed to have an outwardly frontwardly extending shaft  121  portion and a rearward ring gear  122  portion. The ring gear and extending shaft can be two continuously engaged components as in the previous embodiment or by a unitary machined component. The ring gear portion becomes the element of the assembly which is temporarily engaged by the collar gear described below. Thus, the combined extending shaft and ring gear can be referred to collectively as the temporarily engaged shaft, or in this embodiment, the drive shaft. 
     Threaded lubrication holes  125  are sealed by removable threaded plugs  126 . A central friction fitting plug  127  seals the central lumen  28  of the load shaft. Seals  129  seal the junction between the shafts and the housing. A pair of drive fluid intake ports  132  penetrate through the housing wall to supply air or other fluid for activating the clutch. 
     The facing ends  134 , 135  of the shafts internal to the assembly housing are coaxial and splined to have outwardly projecting teeth  136 , 137 . A pilot bearing  181  mounts on the front end of the load shaft  109  within the plug  127  and rotatively supports a corresponding pilot axle  182  extending rearwardly for the rear end of the drive shaft  106 . A wave spring  183  prevents forward axial migration of the bearing out of its seated position in the load shaft. A plural number of permanent magnets  186  can be fitted into a corresponding number of uniformly angularly spaced apart recesses  187  in the rearwardly facing end  134  of the drive shaft so that exposed surfaces of the magnets are located and oriented to capture any ferrous metal wear fragments generated by the engaging and disengaging of the gears. This reduces wear on part which would have been subjected to the fragments. The number and spacing of the magnets is selected to maintain rotational balance of the shaft to which they are fitted. 
     As with the previous embodiment, power is transmitted from the drive shaft  106  to the load shaft  109  by a coaxial internally toothed collar gear  141  also known as a slider gear, also known as an annular clutch, which can reciprocatingly slide coaxially to engage and disengage a driving shaft from a load shaft. The axial movement of the collar gear is controlled by a pneumatically driven system acting on a pair of coaxial annular pistons  151 , 152  rotatively coupled to the collar gear by a pair of coaxial rolling-element bearings  153 , 154 . The pistons move axially within a pair of coaxial annular chambers  155  (hidden), 156  formed by a pair of coaxial annular piston housings  157 , 158  located astride the axial range of movement of the pistons. Sealer rings  160  form substantially hermetic seals between the pistons and their respective piston housings and between the piston housings and the assembly housing. 
     Guide pins  161  restrict angular movement of the pistons with respect to the housings while allowing axial movement. Eight piston-to-piston guide pins  185  engage corresponding holes  162  formed on the facing surfaces  163  of the pistons so that their mutual angular orientation is assured. 
     While the preferred embodiment of the invention has been described, modifications can be made and other embodiments may be devised without departing from the spirit of the invention and the scope of the appended claims.