Abstract:
A gear box for a grass mowing machine with a generally horizontal shaft extending from the engine and/or transmission, and a rotary cutting blade with a generally vertical shaft. The gear box has a top surface and a bottom surface, the gear box enclosing the first end of the generally horizontal shaft and the first end of the generally vertical shaft. The generally vertical shaft extends through the bottom surface of the gear box. The gear box houses a pair of spiral bevel gears to change the transmitting direction from the generally horizontal shaft to the generally vertical shaft. The measurement from the generally horizontal shaft to the bottom surface of the gear box is greater than the measurement from the generally horizontal shaft to the top surface of the gear box.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to gear boxes for grass and vegetation mowers, and more specifically to gear boxes that change the transmitting direction between an engine or transmission, and one or more rotating cutting blades.  
       BACKGROUND OF THE INVENTION  
       [0002]     Grass and vegetation mowing equipment including lawn and garden tractors, zero-turn or spin-turn mowers, and various other mower configurations may have an internal combustion engine or other power supply with a generally horizontal crankshaft, a transmission, and one or more rotary cutting blades mounted to generally vertical shafts. A gear box may change the transmitting direction between the engine and cutting blades. Each cutting blade may be positioned under a mower deck, and the gear box may be located on or above the upper surface of the mower deck.  
         [0003]     A gear box houses pairs of spiral bevel gears to change the transmitting direction from an input shaft to an output shaft. For example, spiral bevel gears and sections of shafts may be disposed at right angles to each other, to change the transmitting direction from a generally horizontal direction to a generally vertical direction.  
         [0004]     A mower operator may be seated or standing on a platform that is on or above the upper surface of the mower deck. The platform may be directly or generally over the gear box. The height of the platform and seat over the deck may result in a high center of gravity for the vehicle and operator, which may present an instability problem. Additionally, the platform may be at such a height above the ground surface so that some operators may find it awkward to step up onto the platform.  
         [0005]     A mowing device is needed with improved stability. A grass mower is needed with an operator platform and seat at a lower height, with a lower center of gravity. A gear box is needed that will help improve the stability of such a vehicle, and lower the center of gravity, operator platform, and seat.  
       SUMMARY OF THE INVENTION  
       [0006]     A gear box transmits power from an engine or transmission with a horizontal shaft, to a cutting blade with a vertical shaft. An input shaft from the engine or transmission is inserted through a first opening in the gear box housing, and an output shaft to the cutting blade is inserted through a second opening in the housing. A first spiral bevel gear is attached to the input shaft and a second spiral bevel gear is attached to the output shaft and is engageable with the first spiral bevel gear. The input shaft has an axis, and the housing is asymmetrical with respect to the axis. For example, the measurement from the input shaft axis to the outer surface of the housing adjacent the second opening may be greater than the measurement from the input shaft axis to the outer surface of the cover. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a cross section view of a gear box according to one embodiment of the invention.  
         [0008]      FIG. 2  is a perspective view of a gear box according to one embodiment of the invention.  
         [0009]      FIG. 3  is a top view of a grass mowing machine with a gear box according to a first embodiment.  
         [0010]      FIG. 4  is a side view of a grass mowing machine with a gear box according to a first embodiment. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0011]     Referring to  FIGS. 1 and 2 , in a first embodiment gear box  10  includes housing  11  and removable cover  12 , with input shaft  13  inserted through first opening  14  in a side of the housing and output shaft  15  inserted through second opening  16  in the bottom of the housing. The housing may have a top that is at least partially open, four sides, and a bottom. The removable cover may be attached to the at least partially open top.  
         [0012]     The input shaft has axis  88 . The output shaft may be perpendicular to the input shaft. The gear box housing may be a metal casting that may be asymmetrical with respect to axis  88 , as will be described in more detail below.  
         [0013]     As shown in  FIG. 3 , input shaft  13  may be operably connected to internal combustion engine  46  through transmission  81 , or to another power supply and/or transmission. The input shaft may have a generally horizontal orientation, and one or more joints may be included between engine  46 , transmission  81  and gear box  10 .  
         [0014]     Referring again to  FIG. 1 , the input shaft may be generally cylindrical in cross section with first end  17  and second end  18 . First section  19  of the input shaft may be positioned in the gear box housing, and second section  20  may be outside the housing. First spiral bevel gear  21  may be attached to the first end of the input shaft. Boss  52  may be formed on the input shaft adjacent the first spiral bevel gear.  
         [0015]     Roller bearings  22  and  23  may be positioned in the first opening around the outer circumference of the first portion of the input shaft. Each roller bearing  22 ,  23  may have a generally tapered cone or cup shape. In one embodiment, inwardly extending collar  51  may receive and position roller bearing  23 . Locking rings  53  and  54  may restrict axial motion of the input shaft and/or one or both of the roller bearings. Annular cap  58  may be positioned in the first opening in outwardly extending collar  72  around the input shaft.  
         [0016]     The output shaft also may be generally cylindrical in cross section, have a generally vertical orientation, and first end  24  and second end  25 . The second end of the output shaft may face downwardly when the gear box is in a mower. The first end may be in the housing at a position adjacent the inner surface of cover  12 . The output shaft may be operably connected to a pulley and or at least one rotary cutting blade. For example, a rotary cutting blade may be directly mounted to second end  25 . Alternatively, one or more pulleys may be mounted to the output shaft at or adjacent the second end thereof, and one or more belts may be wound around the pulley(s) to drive one or more cutting blades mounted to vertical shafts extending below the mower deck.  
         [0017]     Second spiral bevel gear  26  may be attached to the output shaft in the housing. The second spiral bevel gear may have teeth to mesh with the teeth of the first or input spiral bevel gear. The second spiral bevel gear may have a different diameter and number of teeth than the first spiral bevel gear, so as to provide a desired speed ratio between the input and output shafts.  
         [0018]     In one embodiment, the output shaft may have one or more variations or steps in its outer diameter and circumference. For example, from the first end, the output shaft may have first section  27  with a first diameter, second section  28  with a second diameter, and third section  29  with a third diameter. Optionally, the third section may have a diameter that is at least partially tapered. The first and second sections of the output shaft may be enclosed in the housing. The third section may be at least partially in the housing and extend at least partially outside the housing. In one embodiment, the diameter of the first section of the output shaft may be about 25 mm, the diameter of the second section may be about 32 mm, and the diameter of the third section may be about 25 mm.  
         [0019]     Roller bearing  30  may be positioned in the housing at or adjacent removable cover  12  and around the outer circumference of the first section of the output shaft. Roller bearing  31  may be positioned in second opening  16  around the outer circumference of third section  29  of the output shaft. The second opening of the housing may have outwardly facing collar  73 . Locking ring  56  may be captured in a groove in the second opening to restrict motion of roller bearing  31 . Annular cap  57  may be positioned in the second opening around the output shaft.  
         [0020]     In one embodiment, removable cover  12  may have an inner surface  32  and an outer or top surface  33 . The top surface of the cover may face upwardly when the gear box is in a mower. Cover  12  may also have one or more peripheral flange portions  34 , with one or more holes extending therethrough. Threaded fasteners such as cap screws  36  may be inserted through each hole. The outer periphery of the gear box housing may have internally threaded openings  37  into which the threaded fasteners may be inserted.  
         [0021]     In one embodiment, the inner surface of the cover may have inwardly extending collar  38  for receiving and positioning roller bearing  30 . The inner surface of the cover also may have an internal recess  39  dimensioned to provide adequate clearance space for input bevel gear  21 . Collar  55  also may extend inwardly from the housing to receive and position roller bearing  31 .  
         [0022]     The gear box housing may have one or more cup-shaped plugs  40  that seal openings in the housing. The gear box internal volume may contain or be at least partially filled with lubricating oil, which may be accessed through plug  74 . The housing also may include one or more internally threaded fasteners  68  that may be used to secure the gear box to a mower.  
         [0023]     As mentioned above, the gear box housing may be asymmetrical with respect to axis  88  of the input shaft, and this may be observed or determined by one or more measurements. For example, it may be measured as a difference between the internal volume of the gear box housing on each side of axis  88 . In the orientation of  FIG. 1  in which the input shaft has a generally horizontal orientation, the internal volume of the housing below the horizontal axis of the input shaft is shown as V a . The internal volume of the housing above the horizontal axis of the input shaft is shown as V b . In the embodiment shown, V a  is greater than V b .  
         [0024]     Alternatively, asymmetry of the gear box housing may be seen as a difference in length between measurements from the axis of the input shaft to the outer top and bottom of the housing (with the removable cover attached). In the orientation of  FIG. 1 , the measurement from the axis of the input shaft to the bottom of the housing (adjacent the second opening) is shown as L a . The measurement from the axis or center line of the input shaft to the top of the removable cover is shown as L b . In one embodiment, L a  is longer than L b , and most preferably L a  is at least about twice the length of L b . For example, in the embodiment of  FIG. 1 , L a  is about 75 mm and L b  is about 35 mm.  
         [0025]     Now referring to  FIG. 4 , gear box  10  is shown mounted on or over mower deck  45  of grass mowing machine  80 . The mower deck may be raised or lowered with hangers  78  which may be attached to platform  49 . The mower deck in  FIG. 4  is shown in a raised position. The mower deck is positioned longitudinally between front wheels  75  and rear wheels  76  of the mower. The gear box is positioned between the mower deck and platform  49 . Operator seat  60  and control devices  77  are positioned on or above the operator platform, at least partially over the mower deck.  
         [0026]     Referring back to  FIG. 3 , pulley  66  may be driven by the output shaft of gear box  10 . Belt  47  may be wound around pulley  66  to drive other vertical shafts with cutting blades under mower deck  45 , through pulleys  48 .  
         [0027]     Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.