Patent Publication Number: US-6902382-B2

Title: Gear motor start up control

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to hydraulic motors. 
   1. Field of the Invention 
   Hydraulic motors are well known for converting fluid energy into mechanical energy in a system. Hydraulic motors may comprise a number of different basic configurations but a widely used type of motor is one known as a gear motor. A gear motor uses a pair of intermeshing gear elements rotating within a housing. High pressure fluid delivered to an inlet induces rotation of the gear elements and causes a corresponding rotation of a shaft connected to one of the gear elements. Such motors are relatively inexpensive and are capable of handling relatively high pressures. 
   2. Summary of the Invention 
   To improve the efficiency of the motor, the end faces of the gear sets are sealed with a pressure compensating seal assembly in which the pressure of the fluid delivered to the inlet is applied to the seal to ensure close contact with the end faces. Whilst this arrangement improves the efficiency of the motor in use, it can lead to difficulties in initial starting of the motor. The high contact force provided by the pressure compensated seal inhibits rotation of the motor, particularly where the motor is connected to high inertia loads such as a cooling fan or mower reel. 
   3. Description of the Prior Art 
   It is accordingly an object of the present invention to provide a motor which the above disadvantages are obviated or mitigated. 
   In general terms, the present invention provides a gear type hydraulic motor in which pressure fluid is introduced in discrete areas between the gear faces and a pressure compensated seal to improve lubrication upon start up. 
   According therefore to the present invention there is provided a hydraulic motor comprising a housing having a fluid inlet, a fluid outlet and a cavity therebetween. A pair of intermeshing gear elements are rotatable in the housing about mutually parallel axes. Each of the gear elements have a set of gear teeth disposed about the periphery of the element and a support shaft extending from oppositely directed end faces of the set of gear teeth. A bearing assembly is located on opposite sides of the cavity in the housing to support the shafts for rotation about respective ones of the axes. Each of the bearing assemblies has a sealing face overlying the end faces and biased into engagement with the end faces by a pressure compensating seal located between the bearing and the housing. The sealing face has a channel extending partially about the shaft and a fluid communication with the inlet to introduce fluid under pressure between the faces. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which: 
       FIG. 1  is an exploded perspective view of a hydraulic motor. 
       FIG. 2  is a view on the line  2 — 2  of  FIG. 1 . 
       FIG. 3  is a perspective view on an enlarged scale showing the bearing and seal assemblies of the motor. 
       FIG. 4  is an end view of a bearing block shown in  FIG. 3 . 
       FIG. 5  is a view on the line V—V of  FIG. 4 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring therefore to  FIG. 1 , a hydraulic motor generally indicated  10  has a body  12  with an internal cavity  14 . A pair of end caps  16 ,  18  are connected to the housing  12  through bolts  20  and pins  22 . A seal  24  between the end caps  16 ,  18  and housing  12  provides a hydraulically sealed unit. 
   Fluid is introduced into the cavity  14  through an inlet  26  and flows out of the cavity through a similar outlet duct  27  ( FIG. 4 ) on the opposite wall. End cap  16  also houses a pressure relief valve assembly  28  to avoid excess pressure in the cavity  14 . The cavity  14  houses motor elements collectively indicated at  30 . The motor elements are best seen in  FIG. 3  and comprise a pair of gear elements  32 ,  34 . Each of the gear elements has a set of gear teeth  36 ,  38  disposed about respective shafts  40 ,  42 . The sets of gear teeth  36 ,  38  have radial extending end faces  44 . 
   The shafts  40 ,  42  are supported at opposite ends in bearing  46 ,  48 . Each of the bearings  46 ,  48  is similar and has a planar end face  50  arranged opposite the end faces  44 . The shafts  40 ,  42  are received in respective cylindrical bores  52  and the bearings are a sliding fit in the respective end caps  16 ,  18 . The oppositely directed face  54  of the bearings  46 ,  48  supports a pressure compensating seal assembly  56 . The seal assembly  56  has tangs  58  located in notches  60  on the bearing to maintain it in position. 
   As can better be seen in  FIG. 2 , the seal  56  and bearings  46 ,  48  are located within the cavity  14  so that the sets of gear teeth  36 ,  38  are inter-engaged for conjoint rotation. One end of the shaft  42  projects through a bore in the end cap  18  and is sealed by a shaft seal  62 . 
   Referring once more to  FIG. 3 , and to  FIG. 4 , the end face  50  of each of the bearings is formed with a channel  64  that extends from a groove  66  in opposite directions about each of the shafts  40 ,  42 . The groove  66  opens onto the high pressure side of the motor  10 , that is in fluid communication with the inlet  26 , and the channel  64  extends partially about the shaft and terminates prior to the lower pressure zone adjacent the outlet  27 . In the preferred embodiment, the channel  64  is located between the root diameter  35  and major diameter  37  of the tooth and in the embodiment shown is centered on the pitch circle  39  of the gear sets  36 ,  38  so as to be partially covered by each tooth of the gear. The channel  64  extends over an arc in the order of 165° to 220° although in general, the arc should extend sufficiently about the shaft to terminate just prior to the connection of fluid contained within adjacent gear teeth with the low pressure zone hydraulically connected to the outlet. In one embodiment, the channel  64  extends 55° beyond a line joining the centres of rotation of the shafts  40 ,  42 , indicated by the arc in  FIG. 4  so as to terminate prior to the point at which the housing and gear teeth separate adjacent the outlet  27 . The width of channel  64  is selected to provide sufficient area to counter balance the forces imposed by the pressure compensated seal  56  and, in a particular embodiment tested, a width of between 0.8 mm and 1.1 mm extending on a radius between 12.7 mm and 13.0 mm over an arc of 220° measured from the root of the grove  66  provided a effective surface area of 74 mm 2 . The depth of the channel  64  was 1.5 to 1.0 mm. 
   In operation, high pressure fluid is introduced into the inlet  26  and, through action on the gear sets  36 ,  38  causes rotation in opposite direction of the shafts  40 ,  42 . Fluid from the inlets is delivered to the pressure compensating seal assembly that biases the bearings  46 ,  48  toward the end faces  44  of the gear sets  36 ,  38 . Pressure fluid is also delivered to the notch  66  and carried in the channel  64  about the shaft to counter the force of the pressure compensating seal. The channel  64  also permits lubricant to flow between the end faces  44  and the face  50  of the bearing and provide lubrication in a controlled manner to the end faces. Accordingly, upon start up of the motor  10 , the clamping force induced by the seal  56  on the end faces  44  is reduced by the force exerted from fluid in the channel  64  and the presence of lubricant at the end faces. 
   As may be seen from  FIGS. 4 and 5 , the location of the channel  64  between the root diameter  35  and major diameter  37  of the tooth permits the fluid to flow between the faces of the teeth  36 ,  38  and the end face  50  to provide lubrication to each of the teeth  36 ,  38 . A location on the pitch circle  39  diameter has been used in testing. 
   In testing conducted with a motor having a capacity of, A, it was found that the starting torque was decreased by 15% to 29% with a channel  64  of the dimensions detailed above. It will be seen therefore that by providing the channel  64  in the end faces of the bearings  46 ,  48  start up of the motors is facilitated. 
   Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention as outlined in the claims appended hereto.