Abstract:
A lawn mower includes a front wheel suspension system as well as a rear wheel suspension system. A load compensation adjuster is employed as part of the rear wheel suspension system that compensates for riders having significantly differing weights, as well as for weight changes occurring during the mowing operation, such as from grass clippings accumulating in a grass catcher bag.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part patent application of (1) copending U.S. patent application Ser. No. 09/359,537 filed on Jul. 22, 1999 which in turn is a continuation-in-part patent application of (i) copending U.S. patent application Ser. No. 09/144,499, filed Aug. 31, 1998, which in turn claims benefit from Provisional Patent Application Ser. No. 60/063,362 filed on Oct. 28, 1997; (ii) copending U.S. patent application Ser. No. 09/119,818 filed on Jul. 21, 1998, which in turn claims benefit from Provisional Patent Application Ser. No. 60/053,403 filed on Jul. 22, 1997 and Provisional Patent Application Ser. No. 60/063,362, filed on Oct. 28, 1997; and (iii) U.S. patent application Ser. No. 08/898,801, filed on Jul. 23, 1997, which in turn claims benefit from Provisional Patent Application Ser. No. 60/022,865 filed on Jul. 26, 1996; and (2) copending U.S. patent application Ser. No. 09/119,818, filed on Jul. 21, 1998, which in turn claims benefit from Provisional Patent Application Ser. No. 60/053,403 filed on Jul. 22, 1997 and Provisional Patent Application Ser. No. 60/063,362, filed on Oct. 28, 1997, all of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention pertains to the field of lawnmowers. More particularly, the invention pertains to lawnmowers of the riding type having rear wheel independent suspension. 
     BACKGROUND OF THE INVENTION 
     The present invention is described with respect to its use on riding lawn mowers, particularly self-propelled machines fitted with rotating blades for cutting turf grasses. In the most favored typical design, the rider sits atop a three or four wheeled machine, while one or more blades rotate about a vertical axis within a mower deck mounted at the underside of the machine, to cut grasses as the machine moves across the surface being mowed. 
     In many typical riding mowers, the cutter deck is configured as either a ground-following deck or a floating deck. A ground-following deck typically rides on either two or four caster wheels and follows the contours of the ground. A floating deck is hung between the front and rear wheels and beneath the chassis by chains, links or other devices, being adapted to rise up when skids, wheels, rollers and the like attached to the underside of the deck make contact the lawn surface. Generally, the intent for such deck suspension system is to avoid continuing contact with the earth surface. The distance of the cutter deck from the earth surface is determined by the elevation of the chassis. When the mower crosses an earth-surface rise which is relatively severe, that is, short in horizontal length compared to the wheel base of the mower and great in height compared to the pre-set elevation of the mower deck, the deck frequently makes contact with the earth surface. Then, it is intended that the deck rises or “floats” upwardly, so the rotary blades do not hit the earth surface. Such designs work well for many kinds of unevenness, but scalping for certain earth surfaces and mower movements is still a problem. Even if there is no scalping, a variation of the height of the cutter deck relative to the earth surface is not wanted, as it varies the height of the cut grass. 
     Many typical prior art mowers have the wheels rigidly attached to the chassis. Thus, unevenness in the earth surface imparts a lot of up and down chassis motion. Some prior art mowers employ center-pivoting axles which somewhat reduce the vertical motion of the chassis when one wheel encounters unevenness. The related applications describe a preferred transmission steerable mower which has rear drive wheels which are independently driven and spring suspended from the chassis, and which has free pivoting caster front wheels, mounted at the outer ends of a pivotable axle or subframe. The cutter deck is suspended between the front and rear wheels. 
     Mowers with improved spring suspension systems reduce the amount of chassis motion when one or both drive wheels of a mower encounter unevenness in the surface being mowed. Drive wheel traction is improved. However, depending on the particulars of any non-rigid suspension system, the chassis is enabled to roll relative to the earth surface, such as, for example, when the mower is sharply turning or when the mower is traversing a steep hillside. When a mower rolls, a floating cutter deck moves closer to the earth surface and there can be a tendency for scalping of the turf by the cutter deck. An improvement in one of the related applications connects the cutter deck with the rear wheels, thereby ensuring that the cutter deck moves relative to the wheels and ground instead of relative to the chassis of the mower. 
     A problem still exists with the independent suspension system of the related applications. For heavier weight riders or mower accessories, such as grass catchers, the spring used in the suspension system limits the suspension. Rider discomfort occurs when the spring bottoms out. In addition, the collapsed spring can create coil bind which drastically reduces the life of the spring. Merely substituting a stiffer spring for the existing spring causes a harder ride when the load is light. A suspension that works effectively with a wide range of weight variations is therefore needed. 
     SUMMARY OF THE INVENTION 
     Briefly stated, a lawn mower includes a front wheel suspension system as well as a rear wheel suspension system. A load compensation adjuster is employed as part of the rear wheel suspension system that compensates for riders having significantly differing weights, as well as for weight changes occurring during the mowing operation, such as from grass clippings accumulating in a grass catcher bag. 
     According to an embodiment of the present invention, a mower includes a main frame; first and second rear wheels; and first and second rear suspension systems connecting the first and second rear wheels, respectively, to the main frame, wherein the first and second rear suspension systems each include a load compensation adjuster. 
     According to an embodiment of the present invention, a mower includes a main frame; first and second rear wheels; first and second rear suspension systems connecting the first and second rear wheels, respectively, to the main frame; wherein each of the first and second rear suspension systems includes a motor mount effective for mounting a motor; first and second upper links; first and second lower links; the first upper link and the first lower link pivotably connected on one end to a first vertical strut, the first vertical strut connecting an upper frame member of said main frame to a lower frame member of the main frame; the first upper link and the first lower link pivotably connected on another end to the motor mount; the second upper link and the second lower link pivotably connected on one end to a second vertical strut, the second vertical strut connecting the upper frame member to the lower frame member; the second upper link and the second lower link pivotably connected on another end to the motor mount; a spring bracket on the upper frame member between the first and second vertical struts; a rear suspension spring connected between a spring bracket and either the motor or the motor mount; and a load compensation adjuster connected inside the rear suspension spring. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a perspective view of a lawn mower having a front suspension system according to an embodiment of the present invention. 
     FIG. 2 shows a side elevation view of the lawn mower of FIG.  1 . 
     FIG. 3 shows a sectional perspective view of the front suspension system of the present invention. 
     FIG. 4 shows a sectional perspective view of the front suspension system of the present invention. 
     FIG. 5 shows a front elevation view of the lawn mower of FIG.  1 . 
     FIG. 6 shows a partial perspective view of a rear suspension system according to an embodiment of the present invention. 
     FIG. 7 shows a partial perspective view of a portion of the rear suspension system of FIG.  6 . 
     FIG. 8 shows a partial side elevation view of a portion of a rear suspension system according to an embodiment of the present invention. 
     FIG. 9 shows a partial rear elevation view of a portion of the rear suspension system of FIG.  6 . 
     FIG. 10 shows a partial rear elevation view of a portion of a rear suspension system according to an embodiment of the present invention. 
     FIG. 11 shows a partial sectional view of a pre-compressed spring used a the rear suspension system according to an embodiment of the present invention. 
     FIG. 12 shows a cutaway view of an embodiment of a load compensation adjuster according to an embodiment of the invention, wherein the load compensation adjuster is a suspension spring with an overload spring installed inside, as installed in the rear suspension system of FIGS. 6,  7 , and  9 . 
     FIG. 13 shows an elevation view of the load compensation adjuster of FIG.  12 . 
     FIG. 14 shows an elevation view of a shock absorber embodiment of the load compensation adjuster of the present invention. 
     FIG. 15 shows an elevation view of an air shock embodiment of the load compensation adjuster of the present invention. 
     FIG. 16 shows an elevation view of an airbag embodiment of the load compensation adjuster of the present invention. 
     FIG. 17 shows an elevation view of an airbag embodiment of the load compensation adjuster of the present invention. 
     FIG. 18 shows a partial view of a front or rear suspension system according to an embodiment of the present invention. 
     FIG. 19 shows a partial view of a front suspension system according to an embodiment of the present invention. 
     FIG. 20 shows a perspective view of a mower with an embodiment of a front suspension system according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1-2, a lawn mower  10  includes a seat  12  connected to a chassis  14 . Chassis  14  in turn rests on a main frame  16 . Two rear wheels  18  are connected to main frame  16  by the independent suspension (not shown) as described in co-pending U.S. patent application Ser. No. 09/119,818. Two front wheels  22  are connected to main frame  16  via a front suspension system, shown generally at  24 . A floating cutter deck  20  is preferably suspended beneath main frame  16  by rear suspension chains  26  and front suspension chains  28 . Each rear suspension chain  26  is preferably connected to a rear wheel bracket  30  which is “wheel-side” of the rear independent suspension system. Each front suspension chain is preferably connected to a deck height adjustment mount  32  which is part of front suspension section  24 . Suspending cutter deck  20  from the “wheel-side” of the front and rear independent suspensions ensures that cutter deck  20  moves vertically up and down in response to the vertical motion of front wheels  22  and rear wheels  18 , which in turn are responsive to the terrain being mowed. Scalping and uneven cuts of the grass are thus prevented. 
     Although the mower of the present invention can be equipped with either a ground-following cutter deck or a floating cutter deck, using a floating cutter deck with a mower having independent suspension requires additional considerations. Rolling of a lawn mower chassis is induced under certain situations. Among them are: (a) when the mower changes direction while traveling forward and centrifugal force acts laterally at the center of gravity of the machine; (b) when the mower traverses a slope and the gravitational force vector shifts direction relative to the plane of the mower wheel tread, and (c) when the mower travels over a surface undulation, lifting or lowering one or both wheels on one side, thereby rotating the mower chassis in space. 
     Conventional mowers typically use wheels that are rigidly connected to the chassis. In these mowers, the chassis cannot roll relative to the wheels; therefore, there is no rolling of types (a) and (b). Other conventional mowers have a pivoting front or Tear axle at one end, with an opposing end axle rigidly attached to the chassis. In these mowers, the rigidly attached axle limits the chassis roll which the pivoting axle otherwise permits to the extent the chassis is sufficiently rigid. The mower of the present invention, preferably having both front and rear independent wheel suspension systems, beneficially minimizes any rolling of the machine when a wheel passes over certain small bumps and depressions—type (c) rolling. Nonetheless, larger bumps and depressions can induce rolling. 
     As will be explained below, the suspension configuration of FIG. 9 is prone to rolling of types (a) and (b). If cutter deck  20  of mower  10  is suspended from the chassis, rolling may adversely affect the essential mower function, that is, cutting grass to an even height. In particular, when the chassis rolls and one side moves closer to the earth surface, a cutter deck suspended from the chassis also moves closer to the surface. Therefore, the preferable embodiment of the present invention couples the motion of the cutter deck to the motion of a sprung wheel rather than directly to the chassis, thereby reducing the change in cutter deck height relative to the mowed surface when the chassis rolls. 
     Due to the large cutting width preferred in commercial mowers and the distance between the front wheels  22 , rocks or other uneven terrain features that are avoided by front wheels  22  can damage cutter deck  20 . Cutter deck  20  therefore preferably includes a front roller  34 , a rear roller  36  partially hidden by rear wheel  18  in FIG.  2 ), and front caster wheels  38  that protect cutter deck  20  from damage. 
     Referring to FIGS. 3-5, front suspension system  24  includes a longitudinal suspension strut  40  that is connected to main frame  16  via an upper suspension strut  42  and a lower suspension strut  44 . Front wheel  22  is connected to longitudinal strut  40  via a trunnion  39 . Upper and lower suspension struts  42 ,  44  pivotably connect to main frame  16  at a plurality of main frame pivot points  46  and pivotably connect to longitudinal suspension strut  40  at a plurality of front suspension pivot points  48 . A spring  50  is fixed between a spring bracket  52  of upper suspension strut  42  and a front transverse member  54  of main frame  16  so that upward movement of suspension system  24  compresses spring  50  between spring bracket  52  and front transverse member  54 . Upper and lower suspension struts  42 ,  44  are preferably of equal length so that the suspension travel does not change the perpendicularity of front wheel  22  to the ground. 
     As front wheels  22  move vertically up and down in response to the terrain, the front of cutter deck  20 , being connected to longitudinal suspension strut  40  via adjustment mount  32 , moves vertically up and down in response to the vertical motion of front wheels  22 . Main frame  16  is isolated from the vertical motion of front wheels  22  by front suspension system  24 . 
     Referring to FIGS. 6-9, a rear suspension system for mower  10  includes a motor mount  86  connected to main frame  16  via upper links  62  and lower links  64 . Two struts  78  join an upper frame member  74  of main frame  16  to a lower frame member  76  of main frame  16 . Upper and lower links  62 ,  64  are connected to struts  78  at main frame pivot points  66  and to motor mount  86  at rear suspension pivot points  68 . Upper and lower links  62 ,  64  are shown in this embodiment as being of equal length. A spring  72  is captured between a spring bracket  70  of upper frame member  74  and a motor  80 . FIG. 8 additionally shows an optional disk  84  on a wheel hub  82  that is used with disk brakes instead of the more conventional band-drum brakes typically used on prior art lawn mowers. 
     Referring specifically to FIG. 9, a roll center is an imaginary point about which a mower with movable suspension elements tends to roll when subjected to lateral forces. A roll axis of the mower runs through the front and rear roll centers. The location of a roll center R for the rear wheel suspension system is determined by examining the intersection of an upper link phantom line  90  and a lower link phantom line  89 . Line  90  runs through the pivot points for upper link  62  while line  89  runs through the pivot points for lower link  64 . A ground contact phantom line  88  runs from a ground contact point  92 , representing the contact between rear wheel  18  and ground  94 , to the intersection of lines  90  and  89 . In the embodiment described above, where upper and lower links  62 ,  64  are of equal length, lines  90  and  89  intersect at infinity. Line  88  therefore intersects lines  90  and  89  at infinity; line  88  is thus parallel to lines  90  and  89 . The intersection of line  88  with a vertical plane passing through a center of gravity (mass) of the mower is the location of roll center R. 
     In this embodiment, roll center R is substantially lower in elevation than the center of gravity CG of the mower. The location of roll center R can be moved vertically by changing the lengths and angles of the link assemblies. With roll center R significantly below center of gravity CG, the mower tends to sway or rock to the side when turning. Sway bars (not shown), also known as anti-sway or anti-roll bars, are optionally added to this equal-link-length suspension to inhibit swaying during turning. Such bars are typically torsion bars or other elastic structure which, when one wheel moves closer to the chassis, resist such motion with a force, the reaction to which is applied to the opposite wheel. Notwithstanding the tendency to roll, the FIG. 9 suspension provides a better vehicle ride and absorption of bumps compared to an unequal link-length suspension. The FIG. 9 suspension also minimizes lateral motion when the mower load changes, such as when an operator mounts or dismounts the mower, removes a grass-catcher bag, or when there are changes in the mower&#39;s vertical momentum due to uneven terrain. 
     Referring to FIG. 10, an embodiment is shown with unequal link lengths. An upper link  62 ′ is shorter than a lower link  64 ′, with the lengths of links  62 ′,  64 ′ preferably determined such that the roll center R and the center of gravity CG substantially coincide. As shown in the figure, phantom lines  90 ′ and  89 ′ intersect at R, so ground contact line  88 ′ intersects the vertical plane passing through the center of gravity CG at the center of gravity CG. This configuration minimizes the roll tendency of the mower during turning. 
     Referring to FIG. 11, a way of pre-compressing spring  72  is shown. Pre-compression is desirable to lessen the movement of the mower chassis when the mower operator mounts and dismounts the mower. Pre-compression is preferably accomplished by pivotably attaching a threaded guide rod  96  to motor  80 . Rod  96  extends through a hole  97  in spring bracket  70  with a nut  98  on the threaded end of rod  96 . Nut  98  is preferably adjustable so that the amount of pre-compression can be changed when required. 
     Referring to FIGS. 12-13, a load compensation adjuster such as overload spring  100  is installed inside spring  72 . If suspension spring  72  is a closed, ground end, compression spring with a right hand helix, overload spring  100  is preferably a closed, ground end, compression spring with a left-hand helix. Overload spring  100  fits inside spring  72  and is approximately one inch shorter in length than spring  72 . The shorter length of overload spring  100  allows spring  72  to operate at its existing rate, but when spring  72  is compressed more than one inch, overload spring  100  begins to help carry the extra weight. Overload spring  100  is preferably wound with coils in the opposite direction from spring  72 . 
     The characteristics of the preferred embodiment of overload spring  100  is detailed in Table 1. 
     
       
         
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
             
             
               
                 Spring type 
                 compression spring, closed and grounded 
               
               
                   
                 end 
               
               
                 Material 
                 chrome silicon 
               
               
                 Wire Diameter 
                 0.2340 in. 
               
               
                 Mean Diameter 
                 1.0160 in. 
               
               
                 Inside diameter 
                 0.7820 in. 
               
               
                 Outside Diameter 
                 1.2500 in. 
               
               
                 Total Coils 
                 15.6984 in. 
               
               
                 Pitch 
                 0.3308 in. 
               
               
                 Pitch Angle 
                 5.9177 deg. 
               
               
                 Weight 
                 0.6120 lbs. 
               
               
                 Free Length 
                 5.0000 in. 
               
               
                 Solid Height 
                 3.6734 in. 
               
               
                 Load Rate (lbs./in.) @ 0 lbs. 
                 5.00 in. (free length) 
               
               
                 @ 150 lbs. 
                 4.50 in. 
               
               
                 @ 300 lbs. 
                 4.00 in. 
               
               
                 @ 398 lbs. 
                 3.67 in. (solid height) 
               
               
                   
               
             
          
         
       
     
     Referring to FIG. 14, load compensation adjustment is achieved using an alternative embodiment such as a shock absorber  102  inside spring  72  in place of overload spring  100 . This arrangement is commonly referred to as a coil-over suspension. 
     Referring to FIG. 15, load compensation adjustment is achieved using an alternative embodiment such as an air shock  104  instead of shock absorber  102 , although not depicted inside spring  72  in the figure. Using air shock  104  allows adjustment of the spring tension by raising or lowering the air pressure, thereby determining the spring load or tension. 
     Referring to FIG. 16, load compensation adjustment is achieved by using an alternative embodiment such as an airbag  106  to replace overload spring  100  inside spring  72 . Airbag  106  can be inflated or deflated for the desired suspension, either by the user of pre-inflated at the factory. 
     Referring to FIG. 17, an alternative embodiment for load compensation adjustment includes an airbag  108  which could replace the spring within a spring combination by acting as a variable compression spring. As the air in airbag  108  becomes compressed, the force required to compress it further increases. 
     Referring to FIG. 18, a torsion bar suspension is shown connected to wheel hub  82  at the left rear wheel location for mower  10 . A first torsion bar  112  is hooked to lower link  64  at one end, while another end attaches to an adjuster  114 , which permits adjustment of the tension of torsion bar  112 . In similar fashion, a second torsion bar  110  is hooked to the lower link  64  on the right side of mower  10 , with the other end of torsion bar  110  being attached to an adjuster  116  which is connected to lower link  64  on the left side of mower  10 . The right side wheel hub and upper and lower links are not shown in FIG.  18 . The torsion bars  110 ,  112  replace the springs  72  to provide the rear wheel suspension. Load compensation is done with adjusters  114 ,  116 . Although the torsion suspension is shown for the rear wheels, it can be used on the front wheels as well. For the front suspension system shown in FIG. 4, front transverse member  54  and springs  50  are replaced by the torsion bars in the manner just described with respect to the rear suspension system. 
     Referring to FIG. 19, an alternative embodiment of the front suspension system includes a torsion bar  118  attached to lower suspension strut  44  near the lower main frame pivot point  46 . Torsion bar  118  is approximately 1.5 to 2.5 feet (45 to 76 cm) long and extends lengthwise to attach to main frame  16 . A similar arrangement provides the front suspension for the other front wheel. 
     Referring to FIG. 20, in another embodiment, a main frame  122  is connected to a pivoting subframe  124  that incorporates a front suspension system. Pivoting subframe  124  includes a left half subframe  124   a  which is hingeably connected to a right half subframe  124   b . Two hinges, such as a front clevis joint  135  and a rear clevis joint  137 , connect left and right half subframes  124   a ,  124   b  to each other. A front pivot pin  146  acts as the clevis pin for front clevis joint  135  while a rear pivot pin  148  acts as the clevis pin for rear clevis joint  137 . Front pivot pin  146  is connected to a front transverse member  147  of main frame  122  via a front pivot plate  142 , while rear pivot pin  148  is connected to a rear transverse member  149  of main frame  122  via a rear pivot plate  144 . 
     A left spring pocket  140   a , connected to an extension of main frame  122 , houses a left spring  138   a  that abuts a front transverse portion  151   a  of left half subframe  124   a , while a right spring pocket  140   b , connected to an extension of main frame  122 , houses a right spring  138   b  that abuts a front transverse portion  151   b  of right half subframe  124   b . Thus, when a left caster wheel  136   a  rolls into a dip, left half subframe  124   a  moves with it, not affecting right half subframe  124   b  or main frame  122 . Similarly, when a right caster wheel  136   b  rolls into a dip, right half subframe  124   b  moves with it, not affecting left half subframe  124   a  or main frame  122 . Thus, three of the four mower wheels are on the ground at any given time, resulting in a stable, smooth ride with little or no scalping caused by the cutter deck. 
     In this embodiment, rear suspension chains  153  for a cutter deck  150  are attached to rear wheel brackets  155  via a cutter deck lift assembly  156 , while front suspension chains  158  for cutter deck  150  are attached via cutter deck lift assembly  156  to main frame  122 . The weight distribution in a lawn mower of this type is approximately 75% in the rear and 25% in the front. Thus, whereas the rear of the cutter deck is preferably connected to the rear wheel brackets instead of the main frame to avoid scalping during sharp turns or over rough terrain, the front of the cutter deck is preferably connected directly to the main frame in this embodiment. 
     Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments are not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.