LAWN MOWER HAVING INDEPENDENT DRIVE WHEEL SUSPENSION AND A MOVABLE CUTTER DECK COUPLED TO WHEEL MOTION

Abstract: A mower (18) has a pair of front caster wheels (22) and a pair of independently suspended rear drive wheels (30). Each drive wheel is mounted on the shaft of a separate drive motor which is fastened to motor mount (49). Each motor mount is connected to the chassis (22) by means of pivotable links (42, 44), to enable up and down wheel motion, respectively resisted and assisted by springs (56). The cutter deck (24) hangs from two front chain suspenders (74) and two rear suspenders (76). The upper ends of the suspender pairs are connected respectively to bell cranks (72, 70). Each rear bell crank (72) is mounted on bracket (55) which is attached to the motor mount (49). Thus, when any wheel (30) moves upwardly due to a rise in the earth surface, the adjacent rear corner of the cutter deck is lifted upwardly.

Description: LAWN MOWER HAVING INDEPENDENT DRIVE WHEEL SUSPENSION AND A MOVABLE CUTTER DECK COUPLED TO WHEEL MOTION TECHNICAL FIELD The present invention relates to lawn and garden machines, in particular, to lawn mowers. BACKGROUND ART In prior art lawn mower designs, the rider sits atop a four wheeled machine powered by an internal combustion engine. Blades contained within a cutter deck suspended from the machine cut grasses as the mower moves across a lawn or other turf. Commercial riding lawn mowers have various drive systems. Among them are transmission-steerable systems, wherein independent hydraulic motors drive the rear drive wheels, while the front wheels are freely pivotable casters. Directional control, or steering, is obtained by differently varying the speed of the two rear wheels. For such type of machines, it is important that good traction be sustained between the rear wheels and the earth surface, especially when the mower traverses a slope, since gravity tends to pivot the front of the mower downhill. It is also important that any lawn mower maintain an evenness of grass cut. Cutter decks are typically either rigidly fixed to the underside of the mower, or they are suspended so they "float" — that is, they hang at a fixed elevation, but move upwardly upon contact with a rise in the soil surface. Lawn mowers are generally intended for use on lawns and other surfaces which are level or gently undulating. In most typical three and four wheel riding mowers heretofore, the wheels are directly fastened to the frame of the mower machine. However, then any vertical force or displacement on a wheel of the mower is transmitted directly to the frame (or chassis) of the machine. The frame of the mower will tilt and rise and fall according to the effects of one of the wheels. So, under certain conditions the chassis vertical motion will undesirably change the elevation of the cutter deck with respect to the lawn being cut. Another undesirable effect of lifting or tilting of the mower chassis is loss of wheel traction which is critically important in transmission steerable machines. Lastly, bumpy up and down motion is discomforting to the operator. In the prior art, designs have been employed to mitigate the adverse effects of lawn undulations. These include front and rear wheel axles which tilt about a center pivot. But, in such designs, when a wheel rises, the center pivot point and the whole end of the frame necessarily also rise, although to a lesser degree than when the wheel is fastened directly to a frame. Therefore, there is a continuing need for further improvements in suspension systems in self-propelled lawn mowers. SUMMARY An object of the invention is to provide lawn mowers with drive wheel and suspension system combinations which minimize unwanted motion of the mower chassis due to turning and to traversing bumps and uneveness. Another object of the invention is to improve the constancy of contact of mower drive wheels with the surface of the earth, when a mower traverses undulating surfaces, particularly in transmission-steered mowers. A still further object of the invention is to reduce the tendency of the cutter deck to scalp a lawn due to rolling of the mower chassis. In accordance with invention a lawn mower has a cutter deck, a prime mover, one or more wheels at one end of the mower chassis, and a pair of drive wheels at the other chassis end powered by the prime mover. Each drive wheel is part of a drive wheel assembly, attached to either side of the chassis by suspension means which comprise a spring. The suspension means enables each drive wheel to move vertically up and down, respectively with and against force exerted by the spring, independently of the movement of the opposing drive wheel. In the generality of the invention, either the front wheels or rear wheels of a mower may be the driven wheels. In one embodiment, the mower has two front wheels and two rear wheels and the cutter deck hangs between them; each rear drive wheel is part of an assembly comprising a motor independently driven by the prime mover, and the mower is steered by varying the relative speed of the opposing drive wheels. In another embodiment, the four wheel mower has front drive wheels and conventional steerable rear wheels; and, the cutter deck is can ilevered from the front end of the machine. In further accord with the invention, the suspension means for a mower is comprised of upper and lower link assemblies which are pivotably mounted at inner ends to the chassis and at the outer ends to the wheel assembly. In one embodiment, the lengths of the upper links and the lower links are equal, and they run parallel. In another embodiment, the links are not parallel, and the lower links are longer than the upper links, preferably to an extent which makes the roll center of the machine lie at the same elevation from the earth surface as the center of gravity of the machine. In another emboidment, the spring of the suspension system is pre-compressed when the machine is static, to thereby lessen the change in elevation of the chassis due to the operator mounting and dismounting the machine. In further accord with the invention, a lawn mower cutter deck is suspended from a mower chassis so that a portion thereof is lifted in response to the upward motion of a nearby wheel, relative to the chassis. More particularly, a mower has opposing wheel assemblies at the front or rear, or both ends, which wheel assemblies comprise wheels which are spring suspended from the chassis. In one embodiment, one end of the cutter deck is suspended by chains or other like suspenders from the chassis; the other end is suspended from lifting brackets which are integral with the wheel mounts of the spring suspended wheel assemblies. In another embodiment, both front and rear ends of the cutter deck are suspended from the chassis. Suspenders run from brackets attached to the wheel assemblies, superceding the support of the front or rear suspenders, and lifting the cutter deck with upward wheel motion. The wheel-motion coupled cutter deck is applied to different types of lawn mowers. In one type, the cutter deck is suspended between the front and rear wheels. The front wheels are freely pivotable caster wheels, mounted at outer ends of a transverse pivotable member, preferably a pivoting subframe; and, the rear wheels are independently suspended, and independently driven to steer the mower. In another type, the front wheels are indpendently suspended and driven by a transmission. The rear wheels are steerable. The cutter deck is mounted beneath a cantilever subframe at the front end of the mower. The front end of the deck is suspended from the subframe. The opposing sides of the rear end of the deck are connected with the front wheel assemblies by suspenders, so the rear end of the deck moves upwardly with upward motion of the front wheels relative to the chassis. The invention reduces the amount of vertical motion of the chassis, for example when the mower traverses uneven ground and one or both drive wheels rise or fall. As a result there is less vertical motion induced into the cutter deck. There is better contact of the drive wheels with the surface when traversing undulations, for transmission steerable machines directional control of under adverse conditions is improved. When either the manuevers of the mower or the unevenness of the surface being mowed induce chassis motion, a resultant effect on the deck which would tend to make it scalp the turf is reduced. BRIEF DESCRIPTION OF THE DRAWING Fig. 1 is a semi-schematic perspective view of a lawn mower having a cutter deck and pivoting front wheel subchassis. Fig. 2 is a skeletal view of the mower of Fig. 1, showing the chassis and front wheel subframe. Fig. 3 is an exploded view of a wheel assembly. Fig. 4 shows the rear part of a chassis, a left-side suspension system comprised of equal length upper and lower link pairs and a coil spring, and the motor mount of a wheel assembly. Fig. 5 is a view of some of the components shown in Fig. 4. Fig. 6 shows details of the motor and hub of a wheel assembly, and their connection to the suspension system. Fig. 7 is an elevation view from the rear end of a chassis like that shown in Fig. 2, where a suspension system has equal length upper and lower links, and shows the relation between the roll center and the center of gravity . Fig. 8 is a view like Fig. 7, showing a suspension system where the lower link pair length is greater than the upper link pair length, and where the roll center is at substantially the same elevation as the center of gravity. Fig. 9 is view like Fig. 6, showing a partial section elevation view of a motor, coil spring, and rod and nut combination, for providing a pre- compression to the spring. Fig. 10 is a view like that of Fig. 5, showing an alternate embodiment suspension system comprising two struts which support a journaled motor mount . Fig. 11 shows a plan view of a one piece link. Fig. 12 is a part-sectional rearward looking elevation view of portions of the mower shown in Fig. 1, showing portions of the left rear drive wheel assembly and link type suspension system. Fig. 13 is a perspective view of a portion of a mower, deck, wheel assembly, and suspension system, where a lifting bracket and chain lifts the rear part of the deck in response to upward wheel motion. Fig. 14 shows a front wheel drive conventionally steered mower having a front-cantilever cutter deck. Fig. 15 shows a portion of the steerable rear wheel mechanism and suspension for the Fig. 14 mower. Fig. 16 is a side elevation view of a mower having a cutter deck hanging from bell cranks, the rear ones of which are mounted on lifting brackets attached to the opposing side wheel assemblies. Fig. 17 is a perspective view of a deck supported by six chains, two of which connect to brackets mounted off wheel assemblies. Fig. 18 is an elevation view from the rear of a mower showing a one-piece spring suspended axle. Fig. 19 is an elevation view from the rear of a mower, like Fig. 7, showing a pivoting one-piece axle with spring-centering. Fig. 20 is a side view of a fragment of a mower showing how a cutter deck is lifted by means of a cable connected to the motor mount of a wheel assembly. Fig. 21 is a side elevation view of a front wheel drive mower having a deck cantilever-mounted from the front of the mower. MODES FOR CARRYING OUT THE INVENTION The invention is described in terms of its application to a 4-wheel transmission steerable mowing machine. Fig. 1 semi-schematically shows a riding lawn mower 18. Fig. 2 shows the same mower with certain parts removed, to expose the chassis configuration. The mower is comprised of a chassis 20 which carries a prime mover 26, an operator seat 28, and a cutter deck 24. The prime mover is a combination of gasoline internal combustion engine coupled to a hydraulic pump. Fluid from the pump is piped to the separate hydraulic motors which turn each rear wheel. The operator sits on the seat 28, atop the chassis. Rear drive wheels 30 are mounted on opposing sides of the rear end of the chassis, by a suspension system described below. Each rear wheel is independently rotated in forward or reverse by a hydraulic motor powered by the hydraulic pump. Manipulation of control arms 29 varies the hydraulic fluid flow to each motor. The operator obtains directional control, or steering, of the mower by varying the relative speed of the two rear wheels. The front end of the chassis is comprised of a subframe (or subchassis) 22 attached at two spaced apart pivot points 34, 36. The subframe pivots about a longitudinal centerline 31 of the mower. Two free-pivoting front caster wheels 32 are attached on opposing sides of the front end of the subframe. A pivoting axle, mounted on the chassis at point 34, may alternately be used. Stated generally, the preferred front end structure of the chassis comprises a pivoting transverse member at the ends of which are mounted wheels. The pivoting front axle or subframe minimizes twisting and lifting of one side of the chassis which otherwise would occur when one front wheel rises or falls, and the to which chassis lifting or twisting will tend to lift a rear drive wheel from the earth surface. Less preferably, a rigid front axle may be used. A floating cutter deck 24 is mounted beneath the chassis between the front and rear wheels of the mower. The deck is suspended by adjustable length chains or other hangers which limit the downward motion of the deck, yet allow the deck to move vertically, such as when the wheels or other parts on the underside of the deck encounter a rise in the earth surface during mowing. The deck suspension is described further below. The chassis 20 is made of square steel tubing. The rear end of the chassis is comprised of a U-shaped upper member 36 and a like lower member 38. Struts 40 connect the upper and lower members where the rear wheel assemblies are suspended from the chassis. See Fig. 4. Each rear wheel is part of a wheel assembly which is connected to the chassis by a suspension system. The exploded view of Fig. 3 shows components of the wheel assembly, namely motor 82 which bolts to motor mount 49, hub 101 which mounts on the shaft 45 of the motor, wheel 30 which bolts onto hub 101, and spring 56 which bears on the motor. An unshown fitting is attached to the motor casing to locate the bottom end of the spring. Parts of the rear end of the mower and a preferred suspension system are shown in Fig. 4. The left side of the mower is typical of the right side. Reference should also be made to Fig. 5-7 and 12. The preferred suspension system is comprised of an upper link assembly and a lower link assembly and a coil compression spring. The upper assembly comprises a pair of links 42, and the lower assembly comprises a pair of links 44, all pivotably mounted at their inner ends off struts 40 at respective pivot points 52, 48. Each upper set of links 42 and lower set of links 44 run parallel, outwardly and downwardly, from the chassis, to pivotably connect respectively to the top and bottom of motor mount 49. The motor mount of the wheel assembly, and thus the wheel assembly as a whole, is pivot pin-connected to the suspension system, as shown. Each suspension system also comprises a wire coil spring 56 which exerts a downward vertical force on the motor, and thus the wheel assembly, by virtue of being captured between the motor 82 and the spring bracket 66 which is joined to the upper member of the chassis. See Figs. 4 and 12. Thus, a static or dynamic load applied to a rear corner of the chassis will compress the spring, and cause the links and wheel assembly at the corner to move upwardly relative to the chassis. A lesser load, as when a wheel crosses a depression in the earth surface, results in opposite effects. While a steel wire coil compression spring is preferred, other resilient-acting devices may be used in substitution, including other types of metal and non-metal springs, pneumatic springs or air cushions, etc. In the claimed invention, the term "spring" is intended to encompass such generality of devices. In one suspension system configuration, shown in Fig. 7, the upper and lower links are of equal length. (A refrence herein to the length of a link is a reference to the length between the pivot point connections of the links.) Fig. 7 is a fragmentary partial-cutaway elevation view of the rear end of the chassis, suspension system, and wheel assembly. The wheel is shown in phantom cross section. The Figure illustrates how the elevation of the roll center R which is characteristic of the rear suspension system relates to elevation of the center of gravity (or mass) CG of the whole machine, for the equal-length link suspension. In a typical commercial transmission steered mower, the center of gravity will be about 50 cm off the surface of the earth, varying with the fuel and operator weight. In the Fig. 7 configuration of suspension, the roll center is significantly lower in elevation than the center of gravity. A roll center is an imaginary point about which a mower with movable suspension system elements tends to roll, when subjected to lateral forces. The roll axis of the mower runs through the roll centers of the front and rear suspension systems. How the roll center is determined is briefly described below. Another suspension embodiment is shown in Fig. 8 which is analogous to Fig. 7. The upper links 42A are unequal in length to the lower links 44A; and, the links are of such dimension and orientation, that the roll axis R substantially coincides in elevation with the center of gravity CG. This configuration produces minimal tendency for the vehicle to roll during turns. Roll center R is at the intersection of the lower phantom line 63 and the upper phantom line 65. Line 65 runs through the pivot points of the upper links. Line 63 runs through the lower link pivot points. Line 67 runs from the center of ground contact 100 which the wheel 30 makes with the surface of the earth 61 to the convergence point of the lines 63, 65. (In Fig. 7, for parallel links, such point is at infinity.) Where the line 67 crosses the vertical mid-plane CP of the system is the roll center. Thus, when mowing and turning, a mower with Fig. 8 suspension will rock little; and, the mower deck will be kept essentially horizontal and at constant elevation with respect to the surface being mowed. While having the roll center and the center of gravity substantially coincide in elevation is in one sense the optimal design, as compromise, less optimal choices of length link can be used. Reference is made again to the equal link length suspension assembly shown in Fig. 7. The equal-length configuration provides a less desirable relationship of roll center to center of gravity, in that the roll center R is significantly below the center of gravity CG. This means that the vehicle can tend to sway or rock to the side when turning. Sway bars, also called anti-sway and anti-roll bars, are optionally added to the equal length suspension to inhibit swaying of the mower in turns. Typically, such bars are torsion bars or other elastic structures which, when one wheel moves closer to the chassis, resist such motion with a force — the reaction to which is applied to the opposing wheel. Notwithstanding its disadvantageous tendency to roll, the Fig. 7 equal- length link suspension system provides better vehicle ride and absorption of bumps, compared to the unequal link suspension. It also minimizes the lateral motion of the wheels when the load changes, as when an operator mounts and dismounts the mower, or when there is a change in vertical momentum of the mower and operator due to the mower traversing uneven ground. In the Fig. 7 embodiment, the parallelogram form of the upper link, strut, lower link, and motor mount, means a wheel moves vertically without change in camber. It is preferred to use a pair of links to make the upper and lower link assemblies, as have been described, inasmuch as such is an efficient design to accomodate the coil spring and motor. But, other connecting structures which achieve the same purpose may be used. For instance, as shown in Fig. 11, a link assembly may be comprised of a solid link member 109 with four journals 113, for mounting on pins at pivot points. The term link assembly should thus be understood to encompass a one piece upper or lower link, multiple upper and lower links, and other structures which function in a manner similar to those described in the preferred link assembly embodiment. Fig. 10 shows an alternate embodiment of independent rear suspension system where vertical motion is obtained by having the motor block slide up and down on guides. In this embodiment, the motor mount 82 has two opposing journals 84 which are slidably mounted on spaced apart parallel cylindrical struts 86. The struts 86 are fixedly mounted on the chassis 20 by mounting brackets 92, 94. Circumscribing the struts 86 are wire coil springs 96. Thus, in use, the mower chassis is supported by the coil springs pressing against the motor mount. In the Fig. 10 construction there is no lateral motion and no camber of the wheel when it moves up and down. Other substitutional suspension mechanisms may be used, including the so-called MacPherson strut. The weight of the operator of the vehicle, and thus in large measure the weight supported by the rear wheels, may vary by 40 kilograms or more. Thus, as shown in Fig. 9, means may be provided for pre-compressing the suspension spring, to thereby lessen the change in elevation of the chassis due to an operator mounting and dismounting the mower. A threaded guide rod 104 is pivotably attached to the motor. The rod runs freely through a hole in bracket 66 and is able to move up and down with the motor 82. Nut 106 is used to draw the rod through the bracket, thereby compressing the spring 56. Fig. 14 shows a front wheel drive, rear-wheel steered, mower 107 with a front-cantilever cutter deck 124. The enclosed chassis 111 contains the prime mover and other mechanisms. The operator sits on seat 126 and by means of steering wheel 128 turns the rear wheels 130 to control mower travel direction. The prime mover rotates the front drive wheels 112, typically through a transmission-differential type drive system. A deck frame 120 is pivotably cantilevered off the front of the chassis at pivot point 118. Caster wheels 122 support the front or cantilever end of the frame on the earth surface. The cutter deck 124 hangs by four chains 114, 116 from the frame 120, which four chains can be fitted with means for the operator to raise and lower the deck relative to the frame, to determine the basic cutting height of the deck. The rearmost chains 116 can be coupled the motion of wheels 112 as described below in connection with Fig. 21. The drive wheels 112 are rotated by rotary shafts of the transmission system, rather than by independent motors. Each front wheel 112 is part of a wheel assembly, and each wheel assembly suspension system is comprised of a spring and equal length link assemblies, like those described for the rear drive wheels of mower 18. Preferably, the rear steering wheels are also spring mounted. Fig. 15 Illustrates the essential elements of one of the two rear wheel systems of the Fig. 14 machine. Wheel 130 is mounted on a bearing at the end of bent swivel-pin 136 which is journaled in sleeve 134. The sleeve is welded to the outer end of pivoting stub axle 132. The stub axle pivots off the chassis 111 which is only schematically illustrated. For changing the travel direction of the wheel, the top of the swivel pin is rotated by unshown mechanisms which run to the steering wheel 128. With the independent suspensions of the types described above, there is no rigid mechanical connection between the motion of one wheel with that of an opposing wheel. If one wheel encounters a rise or depression, it will move against or with the spring force. This either results in a substantial decrease in chassis vertical motion, or even no appreciable motion, compared to chassis motion which occurs in older suspension systems. When both wheels rise or fall simultaneously due to a large bump or depression, there is no inherent vertical motion of the chassis, as there is with the pivotable axle or a fixedly mounted axle. Of course, whether the chassis rises or falls in such an instance is a function of the size of the disturbance and the sprung and unsprung weights of the mower. Small irregularities rapidly traversed will tend to produce mimimum chassis motion. In the independent suspension system comprising equal length links there is slight lateral wheel motion but no inherent change in camber, in contrast to a pivoting axle suspension and an unequal link length suspension. It is undesirable to have the wheel move in lateral directions because such motion can damage the surface of a lawn. With the invention, vertical motion of the chassis is decreased along with undesirable vertical motion of the cutter deck. The effects of bumps are minimized, and frictional wheel contact with the surfce is improved. For types of mowers which have front drive wheels and unpowered rear wheels, the invention will be in general useful, as the Fig. 14 example shows. Thus, reference to front and rear parts of a mower should not be construed as limiting. Likewise, while the preferred mower has the cutter deck mounted between the front and rear wheels, the invention will also be applicable to mowers where the cutter deck is cantilever suspended from the chassis so that it is forward or rearward of the front or rear wheels, respectively. The invention herein may be applied to vehicles having more or fewer than four wheels and to vehicles designed so the operator can walk at the rear, or ride behind on a sulky, or otherwise guide the machine. With reference again to Fig. 1, the particular cutter deck of mower 18 is a floating deck. Familiar in the art, a floating cutter deck comprises a deck which hangs from the chassis by suspenders, in particular, chains, links, or other like means. The deck elevation is pre-set so it hangs under gravity force at an adjustable limit distance from the chassis, which distance determines the elevation at which the blades will cut vegetation when the mower is traversing a horizontal plane. The deck is vertically movable upwardly toward the chassis in response to a vertical force on the deck, as from ground contact or other lifting force. Referring to Fig. 1 and 16, the cutter deck of the invention has adjustable wheels 33 on either side of the front end, a roller 55 at the front end, and a roller 59 at the rear end. The wheels and rollers are adapted to contact the surface being mowed as the mower passes over certain surface bumps and the like, and thereby exert a upward vertical force on the cutter deck. 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. Most mowers use wheels that are rigidly connected to the chassis. Therefore, in those, the chassis cannot roll relative to the wheels and there is no rolling of the types (a) and (b) in the preceeding paragraph. Another class of mowers has a pivoting front or rear axle at one end, and an opposing-end axle rigidly attached to the chassis. In those, the rigidly attached axle may mostly limit the chassis roll which the pivoting axle otherwise permits, to the extent the chassis is sufficiently rigid. The independent rear wheel suspension system described for the mower 18 beneficially minimizes any rolling of the machine when a wheel passes over certain smaller bumps and depressions — type (c) rolling. The pivoting subframe at the front end similarly aids in avoiding such kind of rolling. Nonetheless, larger bumps and depressions can induce rolling. And, because the roll center of mower 18, with the equal-length upper and lower links, is lower than the center of gravity, it is prone to rolling of types (a) and (b) . If the cutter deck of the mower 18 was solely suspended from the chassis, rolling may adversely affect the essential mower function: cutting grass to an even height. In particular, when the chassis rolls and one chassis side moves closer to the earth surface, the suspended cutter deck also moves closer to the surface. The mower 18 is an example of but one mower construction and, as suggested above, rolling can and does occur in other types of mower constructions. Thus, in the invention, the motion of the cutter deck is coupled to the motion of a spring-suspended wheel relative to the chassis, to lessen change in elevation of the deck relative to the surface being mowed when the chassis rolls. When the chassis moves closer to the earth due to action of the suspension system, the deck is raised closer to the chassis, preferably directly proportionaly. In one embodiment of the invention shown in Fig. 16, the left side of the deck 24 hangs by suspender chains 74, 76 attached at their upper ends to front bell crank 72 and rear bell crank 70, respectively. The angled bell cranks 74, 76 are pivotably mounted, and coupled in rotary motion by adjustable length rod 78, so rotation of a bell crank raises or lowers the deck. There is a corresponding set of bell cranks, chains and mechanism on the opposing right side of the mower. Typically, bell crank sets on each side are coupled to each other. Thus, the operator can simultaneously rotate all the bell cranks (by a cable or lever, or other common means, not shown), to select the predetermined or preset elevation at which the deck ordinarily hangs; and, to thus set the basic height to which grass will be cut. In a typical floating deck the predetermined elevation will be set so the deck wheels and rollers will be somewhat above the earth surface, as shown in Fig. 16. When a sufficiently high bump is encountered, part or all of the deck will be thrust upwardly above the preset elevation by force exerted through contact with the earth of the wheels and rollers. One or more of the chains 74, 76 will be made slack. As shown in Fig. 16, the front bell cranks 72 are pivotably mounted on the upper member of the chassis 20. On each side of the mower, rear bell crank 70 is mounted on a triangle shape lifting bracket 55 which is bolted to the motor mount 49 and thus becomes an intergral part of the wheel assembly. Thus, when wheel 30 and motor mount 49 move vertically up relative to the chassis, the adjacent rear portion of the deck is likewise moved upward relative to the chassis, by force transmitted by suspender 76. If the rear bell cranks 70 were instead mounted on the chassis, as in the prior art, when a rear wheel moved upward, the deck would move closer to the earth and undesirably cut too close, or scalp, the earth surface. In another embodiment of the invention, six suspenders act on the cutter deck. See Fig. 13 and 17. Four chains, two front chains 85 and two rear chains 86, suspend the deck in a conventional mode, using pivotable bell cranks for elevation adjustment, like the system described above. All four chains 85, 86 connect to bell cranks which are mounted on the chassis, and are called in this embodiment "hanging suspenders". On each side of the mower, a lifting suspender, chain 57, connects the nearby rear deck portion to a lifting bracket 55 which is integral with the wheel mount 49 and wheel assembly. Thus, when a drive wheel moves upwardly, the chain 57 is tensioned and the rear corner portion of the deck is raised, making adjacent chain 86 slack. When the wheel moves down, the deck will fall under gravity if it is above its preset elevation. If the deck is at the preset elevation, or reaches it, and the wheel moves down, the chain 57 becomes slack, since the downward motion of the deck is limited by the chain 86. A bell crank or another common adjustment means may be employed for chain 57, so its length may be changed to accommodate different preset deck elevations. Other suspenders can be substituted for chains, in flexibly hanging the deck from the chassis or connecting the deck to the wheel assembly. For instance, cables, slides, slotted links, and the like may be used. As used herein, the term suspender refers to an element which transmits tension force and negligible compression force. Since the deck is rigid, when a suspender lifts a portion of the deck to which it is attached, there are other effects. Typically, in the invention the deck has a width greater than its length; and likewise the side-to-side distances between suspenders is greater than the front-to-back distances. Thus, when the rear corner of a deck is lifted, the front corner on the same side will also be desirably lifted — compared to the undesired alternative of lifting the opposing side of the rear end of the deck. In both the Fig. 16 and 13 embodiments, the lifting bracket becomes an integral part of the wheel assembly, simply extending its dimension conveniently forward so it is over the deck; so, the deck is essentially connected to the wheel assembly. While it is preferred to use the simple mechanical bracket and suspender shown in Fig. 13 and 17, other means may be employed for making the motion of a portion of the cutter deck respond in sense with the vertical movement of a wheel. For example, as illustrated by Fig. 20, a cable 226 runs from the motor bracket 49, around pulleys 230 and 228 (mounted on chassis 20) to the deck 24. As another example, an electromechanical displacement sensor is mounted on the chassis to sense wheel assembly upward motion and provide a signal to a control system, whereupon a hydraulic or electromechanical servomotor mounted on the chassis and connected to the deck is commanded by the control system to move the deck vertically up in response to the sensor signal. While the preferred practice of the invention is to use the simple direct connection between the wheel assembly and the cutter deck, so the lift of the deck is directly proportional to the wheel motion, non- proportional connections may be contemplated within the embodiment variations just mentioned. The present invention also will be useful with other mowers having different wheel assembly and spring suspension systems from the preferred independent suspension mower 18 embodiment. For example, as illustrated by the rear-end view of Fig. 18, a mower has a one-piece beam, or rigid, rear axle 102 (which axle can comprise drive train components, such as is the case with a transaxle) at the ends of which there are hubs on which wheels 30 mount. The axle is suspended from the chassis 20 by springs 104 at opposing ends of the axle. Arms and other link type mechanism which keep the axle in axial and lateral position beneath the chassis are omitted for simplicity. Leaf springs may be substituted for the coil springs shown. And, a single spring running transversely, or along the axle length, may be substituted for the individual springs. In the Fig. 18 embodiment, wheels 30 are each spring suspended and go up and down relative to the chassis when the mower encounters undulations. The chassis is able to roll in the same manner as described above for mower 18, assuming a rigid front end axle which does not prevent such. Therefore, in the Fig. 18 embodiment, the cutter deck will be mounted beneath the mower in a similar fashion to that described above for mower 18, so the rear portions of the deck are linked to the outer ends of the axle, and so upward motion of a wheel relative to the chassis modulates the elevation of the adjacent portion of the deck. In another example, the wheels are attached to the outer ends of a center-pivotable rigid rear axle, as shown in Fig. 19. Similarly to the pivotable front axle previously described, the Fig. 19 axle 106 (which may be a transaxle) mounts at pivot point 107 on chassis 20. Coil springs 108 at either end resist pivoting motion and "self-center" the axle to its rest position. The chassis of the Fig. 19 mower is able to roll, again assuming the opposing end axle and chassis stiffness permit. The invention is applied in the same manner as discussed, for Fig. 18 and generally above. The preferred embodiment has been described in terms of a mower which has rear drive wheels, but the invention is equally well applied to a mower which has front drive wheels, and to mowers where the cutter deck is mounted outwardly from the front or rear of the mower. The invention can also be applied to mowing machines where the cutter deck is in part "ground following" rather than "floating"; that is, where one end, typically the front end, of the deck has wheels which are constantly in contact with the lawn being mowed, so the deck front end goes up and down with the up and down of the terrain. Fig. 21 shows the deck-coupling invention applied to mower 111, which is shown without such in Fig. 14. As mentioned, drive wheels 112 at the front end of the mower are spring suspended in one of the several ways. The cutter deck 124 is suspended by four chains 114, 116. The subframe pivotably cantilevers from the front end of the mower from hidden pivot points 118 and has caster wheels 122 at the front. See Fig. 14. For simplicity, the bell crank system which customarily is employed for presetting the vertical elevation is omitted from the drawings. Front chains 114 connect the cutter deck front end to the subframe. Thus, the front end of subframe and deck rise and fall as the wheels 122 rise and fall due to uneven terrain. The rear end of the subframe rises and falls with the motion of the chassis. Therefore, in this aspect of the invention, a lifting bracket 218 mounts off the spring-suspended wheel assembly on each side of the mower; and, chains 116 connect the opposing sides of the rear end of the deck to the respective opposing side brackets, to thereby induce the desired motion in the deck characteristic of the invention. Generally, the invention is described in terms the wheels, which are spring suspended for up and down motion relative to the chassis, being drive wheels. The invention will also be applied to mowers where the spring suspended wheels are non-drive wheels. In a mower where all the front and rear wheels are spring suspended for vertical motion, the invention may be applied so both the front and rear portions of the deck are respectively connected to the front and rear wheel assemblies. While coil springs have been mostly described, torsion bars and other resilient devices (e.g. , air bags, air cylinders, etc. ) may be used instead of coil springs. While mowers having four wheels, spaced apart at front and rear have been described, the invention can be applied to machines which have essentially a tricycle arrangement. It will be understood that (dual or more) wheels may be may be used where single wheels have been referred to.

Claims: CLAIMS 1. A lawn mower comprising: a chassis having a first end and a second end, and wheels connected to each end for supporting the mower on a lawn surface; a cutter deck having opposing sides and a first end and second end, each end corresponding in orientation with the respective ends of the chassis; means for suspending said cutter deck at a predetermined elevation relative to the chassis, wherein a portion of said cutter deck ends is vertically movable upward and downward above said predetermined elevation in response to an upward force or downward force; means for suspending wheel assemblies, on opposing sides of the first end of the chassis; two first wheel assemblies, each wheel assembly comprised of a wheel and connected to the chassis by a wheel assembly suspension means, wherein the wheel and another portion of the wheel assembly are vertically movable up and down relative to the chassis; characterized by means for lifting said portion of the cutter deck end by applying an upward force thereto in response to upward movement of at least one of the wheels of said first wheel assemblies. 2. The lawn mower of claim 1 wherein said means for lifting comprises a lifting bracket attached to each first wheel assembly; and, a suspender connecting said cutter deck portion and each said lifting bracket. 3. The lawn mower of claim 1 wherein the first end and second end are respectively the rear end and front end of the lawn mower; wherein said first wheel assemblies are drive wheels; and wherein the cutter deck is suspended between the front and rear ends of the lawn mower. 4. The lawn mower of claim 1 wherein the wheels of the first wheel assemblies are independently suspended drive wheels; each drive wheel assembly connected to the chassis by means of a spring, so each drive wheel moves vertically up and down relative to the chassis, respectively against and with force exerted by a spring, independently of movement of the opposing drive wheel. 5. The lawn mower of claim 1 further characterized by means for suspending which comprises a transverse member attached to the first end of the chassis at a pivot point, the member pivoting about a longitudinal centerline of the mower; said first wheel assemblies mounted at opposing ends of the member; so that when the wheel of one first wheel assembly moves vertically up and down relative to the chassis, the wheel of the opposing first wheel assembly moves in the opposite direction. 6. The lawn mower of claim 1 wherein the second end and first end of the cutter deck are suspended from the chassis by hanging suspenders; and, wherein, the means for lifting comprises additional lifting suspenders connecting said portion of each first wheel assembly with an adjacent part of the first end of the cutter deck. 7. The lawn mower of claim 1 wherein each said wheel assembly suspension means comprises an upper link assembly and a lower link assembly vertically spaced apart therefrom; each link assembly pivotably connected at an inner end to a pivot point on the chassis and pivotably connected at an outer end to a pivot point on the wheel assembly. 8. A lawn mower comprising: a chassis having a first end and a second end, each end having wheels respectively connected thereto, to enable movement of the mower over the surface of a lawn; a prime mover, mounted on the chassis; a cutter deck, hanging at an elevation above said lawn surface; wheel assembly supension means, attached to opposing sides of the chassis at said first end; characterized by two drive wheel assemblies, each comprising a drive wheel connected to an opposing side of said first end of the chassis by one of said wheel assembly suspension means; wherein, each suspension means comprises a spring, wherein each drive wheel moves vertically up and down relative to the chassis, respectively against and with force exerted by the spring, independently of movement of the opposing side wheel. 9. The lawn mower of claim 8 characterized by each wheel assembly suspension means comprising an upper link assembly, a lower link assembly; each link assembly comprised of at least one link pivotably connected at an inner end to a pivot point on the chassis and pivotably connected at an outer end to a pivot point on the wheel assembly; wherein the spring urges the link assemblies vertically downward. 10. The lawn mower of claim 9 characterized by the upper and lower link assemblies having equal lengths. 11. The lawn mower of claim 8 wherein the chassis first end and second end are respectively the rear and front end of the lawn mower; wherein the first wheel assemblies are connected to the chassis at the rear end thereof; and wherein the chassis has a longitudinal axis; further characterized by a subframe pivotably connected to the front end of the chassis, for pivoting about said longitudinal axis; wherein the wheels at the front end of the chassis are connected to said subframe. 12. The lawn mower of claim 8 wherein the chassis first end and second end are respectively the rear and front end of the lawn mower; wherein the first wheel assemblies are connected to the chassis at the rear end thereof; characterized by a cutter deck suspended between the front and rear ends of the mower; each rear wheel being independently driven by the power from the prime mover; and two caster front wheels, one each attached to opposing sides of the front end of the lawn mower; wherein the steering direction of the lawn mower is controlled by varying the relative speed of the rear wheels. 13. The lawn mower of claim 8 wherein the chassis first end and second end are respectively the front and rear end of the lawn mower; wherein the first wheel assemblies are connected to the chassis at the front end thereof; characterized by a cutter deck cantilevered from the front end of the mower.

Inventors: GORDON TODD B, GORDON, TODD, B.
Applicants: FERRIS IND INC, FERRIS INDUSTRIES, INC.
Application year: 1998
Main classification: A01D34
IPC codes: A01D34, B60G1, B60G3, B60G9, B60K7