Abstract:
A top dresser for distributing particulate matter on a variety of terrain. The top dresser may includes a towable frame which is operatively connected to a pair of wheel assemblies. Each wheel assembly is rotatingly attached to the frame of the top dresser in such a fashion as to enable the wheels of the wheel assembly to follow the contours and undulations in the terrain over which it traverses. Each wheel assembly is operatively connected to a hydraulic pump which is in turn operatively connected to a hydraulic circuit which is used to control and power various elements of the top dresser. The top dresser includes a hopper with gate assembly and a conveyor to distribute particulate matter at predetermined rates to the terrain. The gate assembly is adjustable and includes a biased gate which deflects in response to contact with large nonconformities such as rocks. The conveyor belt is a pre-manufactured substantially continuous loop of material which has a patterned or otherwise roughened surface. The conveyer belt is supported between a pair of roller assemblies, including a drive roller having a textured metal oxide coating for enhancing the friction coefficient between the belt and the drive roller assembly. The conveyor belt and the attendant roller assemblies may be accessed by shifting a portion of the top dresser, and the conveyor belt and attendant roller assemblies may be in turn shifted to permit replacement, repair and inspection. A hydraulic circuit is provided with a charge pump assembly which eliminates the need to maintain a pressurized reservoir, thus reducing leakage during periods of inactivity.

Description:
This application claims the benefit of priority pursuant to 35 USC §119(e)(1) from the provisional patent application filed pursuant to 35 USC §111(b): as Serial No. 60/165,689 on Nov. 16, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to devices for spreading or dispensing particulate matter upon a traversed terrain, and in particular to a device for top dressing turf. 
     2. Description of the Prior Art 
     Top dresser devices utilizing a wide variety of technologies are well known in the art. One particular class of top dressers includes a frame-mounted hopper for receiving particulate matter, a flexible belt for transporting the particulate matter along the hopper, and a brush assembly for dispensing the particulate matter as it is conveyed along the belt. Yet another class of top dressers includes a tow-behind variety, wherein a top dresser device is disposed upon a towable frame and drawn across the terrain by a traction vehicle. Power for the belt and brush assemblies may be external or internal to the top dresser. An external power source may, for example, be an accessed hydraulic system of the traction vehicle. Alternatively, internal power sources may include a separate internal combustion engine or a ground driven mechanism. Generally, the term “ground driven” refers to the interaction of an apparatus as it moves relative to the ground; in this instance, the support wheels of a top dresser as they roll along the ground. Ground driven mechanisms may include systems for mechanically or hydraulically coupling the support wheels of a top dresser to provide power other components of the top dresser during operation. In a hydraulic powered ground driven top dresser, for example, support wheels may be coupled to hydraulic pumps to provide pressurized fluid to drive the top dresser. 
     Prior art top dressers present several substantial limitations. One limitation of hydraulic power based ground driven top dressers is the requirement of an adequate supply of pressurized fluid to the inlet ports of the wheel driven pumps. It has been recognized that inlet fluid pressurization is needed to charge the wheel driven hydraulic pumps to prevent cavitations, dry runs, etc., and for this reason supply reservoirs have been pressurized. Reservoir pressurization presents relatively few problems during top dresser operation. However, reservoir pressurization may promote leakage within the system, particularly at the wheel driven hydraulic pumps whenever the top dresser is inactive. This is particularly problematic because hydraulic fluid may damage turf surfaces. Furthermore, the use of fluidic systems which have pressurized containers may require periodic inspection, certification and/or regulatory compliance before they can be introduced into certain markets. 
     Another limitation of prior art top dressers has been impaired machine operation over uneven or irregular terrain. In such terrain, a tire may temporarily lift away from or “skip” over the ground and tear or scuff the turf when the tire re-contacts the turf surface. Another limitation related to skipping is the uneven distribution of weight that occurs between the adjacent tires when the top dresser traverses over undulating terrain. As the top dresser traverses such terrain and one of the tires is unable to maintain contact with the ground, all of the weight that is normally supported by the adjacent tires must now be supported by the tire(s) which remains in contact with the ground. This reduces the ground contact area and increases the ground contact pressure. Turf rutting or other damage may result as the weight of the top dresser is transferred to the other tires(s) in contact with the ground. 
     Yet another limitation of some prior art top dressers is the inability to evenly distribute material at a substantially consistent predetermined application or coverage rate (e.g., lbs. of top dressing material per square yard of turf) irrespective of the speed at which the top dresser is being moved relative to the terrain. In this regard, in order for the application rate (lbs. per square yard) to be consistent, the distribution rate (lbs. per second) of material exiting the top dresser needs to be proportional to the ground speed (feet per second) of the top dresser. Operation of some prior art ground driven top dressers at varying ground speeds may result in uneven distribution of material upon the turf surface. For example, an application rate greater than desired when the top dresser slows below a nominal operating ground speed, or an application rate less than desired when the top dresser exceeds a nominal operating ground speed. Particular solutions to the problem have included unduly complex regulating mechanisms which are difficult to maintain and prone to breakdown. Known regulating mechanisms may include clutches, chains, and shafts, each of which are especially prone to damage in hostile environments. 
     Another related limitation of some prior art top dressers is the inability to accommodate nonconformities such as large rocks or other debris mixed in with the top dressing material. This is not an unusual or rare occurrence because top dressing material is typically stored outdoors and is susceptible to many forms and sources of contamination. Large rocks or debris contained within a mixture of top dressing material may become lodged at the metering gate mechanism resulting in uneven material distribution and/or damage to the conveyer belt and the gate mechanism. Thus, an operator of a top dresser must not only keep a watchful eye on the distribution rate, but is compelled to periodically stop the top dresser and inspect the gate mechanism for nonconformities. This may result in significant down time even if the inspection does not reveal any nonconformities. One time consuming approach in dealing with nonconformities may be to pre-condition or pre-screen the top dressing material prior to, or during loading of the hopper of a top dresser. Another approach may be to store the top dressing material in a controlled environment. 
     Another limitation of some prior art top dressers concerns the effort required to install a conveyer belt on the top dresser, as during initial manufacture, or replacement of a worn or damaged belt. Initial installation and replacement or repair of worn or damaged belts has generally been a tedious and time-consuming task, at best. Often, a top dresser must be substantially dismantled in order to access a conveyor belt and its attendant roller assemblies. This process may also require specially designed fixtures, equipment and trained personnel to make the necessary repairs and/or replacement, and may result in significant down time. 
     Another limitation of some prior art top dresser concerns the longevity or working life of the conveyer belt. The typical prior art conveyor belt is formed by taking opposing ends of a length of suitable material and joining them together by well known linking or seaming techniques, including mechanical link structures. Conveyer belts often degrade at or near the links, as the structures are generally more rigid than the belt material. Additionally, conveyor belts may fail or be damaged due to imperfections, the use of incompatible linking materials, extremes in temperature, stretching, etc. A need therefore exists for a conveyer belt having improved durability provided by an elimination of a mechanical linking structure. 
     In summary, there is a need for a top dresser with support wheels which do not skip or scuff as they travel along uneven terrain. Still a further need exists for a top dresser which is able to distribute particulate matter at a predetermined application rate irrespective of the speed of the top dresser. A need also exists for a top dresser with a dispensing apparatus which is able to accommodate large nonconformities effectively and efficiently. Additionally a need exists for a top dresser which has a conveyor belt which less susceptible to premature separation and which is easy to access and service. And there is still further a need for a top dresser with a hydraulic circuit which is less prone to fluid leakage during periods of inactivity. 
     SUMMARY OF THE INVENTION 
     A top dresser for distributing particulate matter on a variety of terrain. In one embodiment, the top dresser includes a towable frame which is operatively connected to a pair of wheel assemblies. Each wheel assembly is rotatingly attached to the frame of the top dresser in such a fashion as to enable the wheels of the wheel assembly to follow the contours and undulations in the terrain over which it traverses. Each wheel assembly is operatively connected to a power converter such as a hydraulic pump or an electrical generator which is, in turn, operatively connected to a hydraulic or electrical circuit, as the case may be, which is used to control and power various elements of the top dresser. 
     A top dresser according to the present invention includes a hopper with a metering gate assembly and a conveyor to distribute particulate matter at predetermined rates to the terrain. The gate assembly is adjustable and includes a gate which is temporarily displaced in response to large nonconformities such as rocks. The conveyor belt is a pre-manufactured “seamless” or continuous loop of material having a patterned or otherwise roughened surface for conveying the particulate matter. The conveyer belt is termed “seamless” in that no external link structure is necessary to join the ends of the belt material to form the belt loop. The conveyer belt is movably supported between a pair of roller assemblies, including a drive roller assembly having a metal oxide surface for enhancing the friction coefficient between the roller and the conveyer belt. The conveyor belt and the attendant roller assemblies may be accessed by shifting a portion of the top dresser, and the conveyor belt and attendant roller assemblies may be in turn shifted to permit replacement, repair and inspection. A hydraulic circuit is provided with a charge pump assembly which eliminates the need to maintain a pressurized reservoir, thus reducing leakage during periods of inactivity. 
     Accordingly, it is an object of the present invention to provide an improved granular material spreader that is efficient in operation across a variety of terrain. In particular, a towable top dressing device is provided having a pair of wheel sets or assemblies which may independently follow the contours of uneven terrain. In one preferred embodiment, each pair of wheel sets or assemblies may undergo a “rolling” motion relative to the frame and other wheel set to maintain contact with the ground. It is another aspect of the present invention to minimize the uneven distribution of weight between the wheels of a towed top dresser. 
     It is another object of the present invention to provide a towable, vehicle-mounted, or self-propelled top dresser which evenly distributes material at a substantially constant predetermined coverage rate (e.g., lbs. of top dressing material per square yard of turf) irrespective of the speed at which the top dresser is moved relative to the terrain. In this regard, in order for the application rate (lbs. per square yard) to be consistent, the distribution rate (lbs. per second) of material exiting the top dresser needs to be proportional to the ground speed (feet per second) of the top dresser. 
     Another object of the present invention is to provide an improved gate assembly for permitting the top dresser to distribute top dressing material which may have nonconformities such as rocks or other debris incorporated therein. The improved gate assembly includes a biased gate relief assembly or release device which is temporarily displaceable to permit nonconformities or outsized objects such as rocks and debris to pass thereby with minimal risk of damage to the conveyor belt and gate assembly of the top dresser. In this regard, the top dresser of the present invention is able to use top dressing mixtures which would otherwise require preconditioning prior to application. 
     It is another object of the present invention to provide a ground driven hydraulic power based top dresser having an improved hydraulic circuit for selectively powering a conveyor belt and a brush assembly. An improved hydraulic circuit eliminating the necessity of a pressurized reservoir system is provided in an embodiment of the present invention. Additionally, a feature of the hydraulic circuit is that it is able to assist in braking the utility vehicle and top dresser under some conditions. 
     It is yet another object of the present invention to decrease the amount of down-time by the use of a longer lasting conveyor belt with improved access thereto for maintenance and replacement. 
     These and further objects and advantages of the present invention will become clearer in light of the following detailed description of preferred embodiments in connection with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a ground driven top dresser according to the present invention illustrated in connection with a utility traction vehicle; 
     FIG. 2 is a rear elevation view of the top dresser of FIG. 1; 
     FIG. 3 is a top plan view of the top dresser of FIG. 1; 
     FIG. 4 is a partially cut-away right side elevational view of the top dresser of FIG. 1; 
     FIG. 5 is a front elevational view of the top dresser of FIG. 1 illustrating the ground following capability of the right axle set; 
     FIG. 6 is a left side elevational view of the top dresser of FIG. 1; 
     FIG. 7 is a detailed cross sectional view of a portion of the top dresser of FIG. 2 taken along line  7 — 7  and illustrating the gate mechanism and gate release device; 
     FIG. 8 a  is a schematic view of the gate mechanism of FIG. 7 illustrating the gate mechanism when the distribution rate is at a relatively low setting; 
     FIG. 8 b  is a schematic view of the gate mechanism of FIG. 7 illustrating the gate mechanism when the distribution rate is at a relatively moderate setting; 
     FIG. 8 c  is a schematic view of the gate mechanism of FIG. 7 illustrating a temporary gate displacement as a large nonconformity passes through the gate mechanism; 
     FIG. 9 a  is a schematic side elevational view of the top dresser illustrating access to the conveyor belt and the front and rear roller assemblies; 
     FIG. 9 b  is a schematic front elevational view of the top dresser illustrating replacement of a conveyor belt; and 
     FIG. 10 is a schematic view of a hydraulic circuit for the top dresser of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings wherein like numerals designate like parts throughout, one preferred embodiment of the present invention is illustrated in FIG. 1 as a tow-behind top dresser device  10 . The top dresser  10  includes a frame  12  having a drawbar  14  by which the top dresser  10  may be coupled to a traction or utility vehicle  16  and drawn across a turf surface  18 . One particularly suitable traction vehicle  16  may be, for example, a Toro Workman® utility vehicle manufactured by the assignee of the present invention. While one embodiment of the present invention described herein references a tow-behind top dresser  10  used in conjunction with a traction vehicle  16 , aspects of the invention may be applicable to other types of top dressers, such as vehicle mounted or self propelled devices (not shown), etc., as may be appreciated by those skilled in the relevant arts. 
     The top dresser  10  is preferably rollingly supported upon the ground  18  by a pair of wheel assemblies  20 , each having a pair of wheels  22 . To minimize tire marking of distributed material, the transverse track width between the wheel assemblies  20  is sized in relation to the particulate matter drop zone width. As further discussed herein and as particularly illustrated in FIGS. 2,  4 , and  5 , each wheel assembly  20  is pivotally coupled to the frame  12  about a longitudinal axis  30  which is orthogonally oriented relative to the axis of rotation of the paired wheels  22  of each wheel assembly  20 . This arrangement allows the wheels  22  to follow undulations and contours of the traversed turf  18 . In this regard, each wheel assembly  20  may undergo a “rolling” motion relative to the direction of motion of the frame  12  of the top dresser  10  to maintain contact over a variety of local turf environments. Additionally, each wheel assembly  22  is operatively coupled to a power generator such as a hydraulic motor  32  functioning as a pump for the hydraulic circuit  130  of the present invention. As disclosed herein, power for a movable surface or belt assembly  34  and brush device  36  is developed by the wheel driven pumps  32  and conducted via conventional power transmission conduits of the hydraulic circuit  130  (See, FIG.  10 ). 
     Operator control of the belt and brush assemblies  34 ,  36  may be made via a remote switch  38 , such as a hand-held electric switch providing on-off instructions. As described hereinafter with reference to the hydraulic circuit  130  of FIG. 10, in the preferred embodiment the remote switch  38  may include a  12  volt power lead for activating a solenoid valve component  172  of the hydraulic circuit  130  to initiate movement of the belt and brush assemblies  34 ,  36 . Additionally, user control of the application rate of top dressing material may be made by adjusting the gate assembly  84  as illustrated in FIGS. 7 and 8, and as described below. 
     Again with reference to FIGS. 1 and 3, the top dresser  10  includes a hopper  46  for receiving particulate matter  42  to be distributed. The hopper  46  is disposed upon the frame  12  and includes a plurality of sloping front, rear and side surfaces  48 , an open top or upper portion  50 , and a substantially closed bottom or lower portion  52  in communication with a conveyer belt  54 . Hopper  46  includes a window  53  on its front surface  48  which permits the operator to visually assess the level of top dressing material  42  within the hopper  46  during operation. As described hereinafter with particular reference to FIGS. 9A and 9B, the hopper  46  may be temporarily shifted with respect to the frame  12  and pivoted about pivot points  49  to gain access to the belt  54 , as during maintenance or belt  54  removal. 
     The belt assembly  34  of the present invention preferably includes a “seamless” or continuous conveyor belt  54  lacking any separate mechanical joint or linking structure as provided in prior art top dressers. The belt  54  is preferably a length of PVC/fiber reinforced belt material joined at its ends with a finger or dovetail splicing. The belt joint area proximate the dovetail splicing is rejoined with PVC material and patterned to match the belt material pattern  55 . The patterned or otherwise roughened surface  55  of the belt  54  is for engaging the top dressing material  42  within the hopper  46  and facilitating the conveyance thereof along and out of the hopper  46 . The belt  54  is operatively connected to and rollingly engaged by a front roller assembly  58  and a powered rear roller assembly  60  and is disposed adjacent the bottom of the hopper  46  to receive the top dressing material  42  contained therein. The inwardly facing surface  56  of the belt  54  is in slideable contact with a platen  61  or plate surface situated within the interior region of the belt  54  to support the top dressing material  42  within the hopper  46 . As stated previously, the use of a “seamless” belt is preferred over conventional spliced belts in that it is better able to withstand the environment in which it operates. The preferred continuous belt  54  of the present invention is provided by All-State Industrial Rubber and Belting, of West Des Moines, Iowa. One particular approach to belt  54  replacement is also provided by the present invention and is discussed herein with particular reference to FIGS. 9A and 9B. 
     Front and rear roller assemblies  58 ,  60  each include a pair of bearing assemblies  62  for rotatably and transversely disposing the roller assemblies  58 ,  60  upon the frame  12  of the top dresser  10 . Rear roller assembly  60 , which may be selectively powered by a belt motor  64  of the top dresser hydraulic circuit  130  as further described herein, includes a friction enhancing surface, such as an applied metal oxide surface  66 , for increasing the friction coefficient between the rear roller  60  and the inwardly facing surface  56  of the belt  54 . Other friction enhancing surfaces may also be practicable, including other applied coatings, textured roller surfaces, etc. Belt motor  64  power may be selectively controlled by the operator via the remote switch  38 , as disclosed in FIGS. 1 and 10, and further described herein. 
     Referring particularly to FIGS. 1,  4 , and  7 , the top dresser  10  further includes a brush assembly  36  for engaging the top dressing material  42  and rearwardly propelling it from the belt  54  to the turf surface  18 . The brush  40  of the brush assembly  36  is rotatably disposed upon the frame  12  via brush bearing assemblies  70  and is in substantially parallel alignment with the belt  54  of the belt assembly  34 . The brush  40  is preferably rotatably driven via the hydraulic circuit  130  to work the top dressing material  42  from the patterned belt surface  55 . Operation of the brush assembly  36  may be controlled via operator access to the hydraulic circuit  130  as disclosed in FIG. 10, and further described herein. 
     Various hydraulic circuit  130  componentry of a preferred embodiment of the present invention is illustrated in FIGS. 2 and 4, and includes a pair of low speed high torque (LSHT) wheel driven motors  32  functioning as pumps, a brush motor  72  and a belt motor  64 . Each wheel driven pump  32  is operatively connected to a wheel assembly  20  via a chain  74  and appropriately sized sprockets  75 ,  76 . Preferably, the wheel driven motors  32  have a pumping capacity of approximately 5.4 cubic inches per revolution. It will be appreciated that the fluid output developed for each wheel driven pump  32  varies with the speed at which the top dresser  10  traverses a terrain. The brush and belt motors  72 ,  64  may be fluidly coupled to the hydraulic circuit  130  so as to receive the fluid output from one or more wheel driven pumps  32 . In the illustrated embodiment, brush motor  72  is disposed upon the frame  12  and directly coupled to the brush  40  of the brush assembly  36 , while belt motor  64  is coupled to the rear roller assembly  60  via chain  77  and appropriately sized sprockets  78 ,  79 . The brush and belt motors  72 ,  64  have a preferred input capacity of approximately 2.3 and 29.8 cubic inches per output revolution, respectively. As with the wheel driven motors  32 , it will be appreciated that the fluid output developed at the brush and belt motors  72 ,  64  varies with the speed at which the top dresser  10  traverses a terrain. 
     Referring again to FIGS. 4-6, each wheel assembly  20  is mounted to the frame  12  through longitudinally aligned bearings  80  to permit pivoting movement of the wheel assembly about a longitudinal axis  30  which is parallel to the direction of motion of the top dresser  10  as it traverses a terrain. FIG. 4 is a partial cut-away view illustrating a wheel set  20  and associated bearing  80  assemblies. For enhanced terrain handling and overall stability of the top dresser  10 , the longitudinal axes  30  of the wheel assembly bearings  80  are disposed below (further from the hopper and closer to the ground surface than) the wheel bearing axes  82 . Placement of the longitudinal wheel assembly axes  30  below the wheel bearing axes  82  enhances device stability by preventing undesirable “overcenter” tilting of the wheel assembly  20 . As illustrated particularly in FIG. 5, movement of the left wheel assembly  20  is defined by a range of motion which permits the wheels  22  of the wheel assembly  20  to follow undulations and contours of the traversed turf. As depicted, the wheel assembly  20  may roll approximately ±20 degrees with respect to the top dresser frame  12 . Importantly, each wheel assembly  20  may separately and independently undergo “rolling” type motions relative to the frame  12  of the top dresser  10  to maintain contact over a variety of local turf surfaces. 
     FIGS. 3,  7  and  8  illustrate a gate assembly  84  for metering the top dressing particulate material  42  out of the hopper  46  and providing a release mechanism to permit nonconformities  86  such as large rocks or other debris to pass out of the hopper  46 . Gate assembly  84  includes a pivotable gate  88  coupled to the frame  12  of the top dresser  10  at pivot points  90 . Gate  88  extends transversely across the conveyer belt  54  between a pair of brackets  92 . Referring to FIG. 7, gate  88  is rotatably coupled at each end to a bracket  92  to permit pivot action thereabout. A seal member  94  of rubber or other material is secured to a lower edge of the gate  88  and extends across the belt  54  surface. The rear hopper wall surface  48  extends downwardly ahead of the gate assembly  84  and includes a triangular shaped structure  96  for strengthening the wall against deflection. Defined beneath the triangular structure  96  of the rear wall  48  is an elongate aperture  95  extending transversely across the belt  54 . The aperture  95  is configured so that it effectively limits the maximum distribution rate for top dressing material for the top dresser  10  (as when the gate  88  is raised into its highest position possible (not shown)). 
     As further discussed with reference to FIG. 8, the seal  94  and the conveyer belt  54  define a distance  100  which determines the mean rate of particulate distribution. This distance  100  may be varied by selectively moving the gate  88  of the gate assembly  84 . To facilitate moving the gate, the gate assembly  84  is provided with a gate release device  102  having an adjusting handle  104  and a user manipuable knob  106 . Adjusting handle  104  is received within an elongate rate adjusting channel  108  (See FIG. 3) of the frame and may be user biased within the channel  108  in relation to a calibrated rate scale  110  to vary the distance  100  between the seal  94  and the belt  54  and thus vary the mean rate of top dressing particulate distribution. The adjusting handle  104  is maintained in a selected position relative to the rate scale  110  by slideable gate release plate  112 , and as further discussed with reference to the gate release device  102 . 
     As illustrated in FIGS. 7-8, an additional feature of the gate assembly  84  is that the gate release device  102  which permits a transient deviation in the distance  100  between the seal  94  and the belt  54  in order to allow large rocks  86 , debris or nonconformities to pass therebetween. As a result, the particulate distribution rate of the top dresser  10  may exhibit corresponding transient spike(s) which differ from the preselected mean particulate distribution rate. Gate release device  102  includes the gate release plate  112  which is selectively and slideably coupled to the frame  12  of the top dresser  10  with first and second fasteners  114 ,  116 . The first fastener  114  includes a gate locking knob  118  which the user may manipulate to loosen the gate release plate  112 . Upon loosening the plate  112 , the user may adjust the distribution rate with reference to the rate scale  110 , and then selectively secure the plate  112  in place to fix the distribution rate. Additionally coupled to the gate release plate  112  is a release assembly  120 . Release assembly  120  includes a biasing element  122 , a clevis pin  124  received within the biasing element  122 , and a pin support  126 . Biasing element  122  engages the adjusting handle  104  to urge the adjusting handle  104  away from the pin support  126  and into contact with an edge  128  of the gate plate  112 . Preferably, the biasing element is a spring, however, it is understood that other restorative devices may be used. 
     Referring now to FIGS. 8A-C, operation of the gate assembly  84  may be discussed. FIG. 8A illustrates the gate  88  as having been adjusted into direct or partial contact with the belt  54 . This setting illustrates a relatively low distribution rate setting, as only a small amount of top dressing material  42  will be conveyed through the gate  88  by the belt  54 . FIG. 8B illustrates the gate  88  as having been adjusted away from the low distribution rate setting of FIG. 8A to provide a greater preselected distribution rate. A mean distance  100  is established between the gate seal  94  and the belt  54  to provide the average preselected distribution rate. A nonconformity such a rock  86  having a dimension larger than the mean distance  100  is illustrated as being admixed within the top dressing material  42  of the hopper  46  and being directed toward the gate  88 . Upon contacting the gate  88 , the nonconformity or rock  86  is allowed to pass through the gate assembly  84  and out of the hopper  46  by the gate release device  102  rather than being retained within the hopper  46  and potentially damaging the belt  54  and/or gate  88  or even disrupting the distribution flow. As illustrated in FIG. 8C, the nonconformity  86  temporarily displaces the gate  88  from its preselected distribution rate setting about its pivot points  90  to increase the distance  100  between the gate seal  94  and the belt  54  a sufficient amount to allow passage therethrough. Note that as the nonconformity encounters and moves past the gate  88 , it deflects the seal  94 . As the gate  88  pivots, the biasing element or spring  122  is compressed between the gate adjusting handle  104  and the pin support  126 . After the nonconformity  86  has passed through the gate assembly  84 , the gate  88  is urged back into its preselected rate position by action of the biasing element or spring  122 . As may be appreciated by those skilled in the relevant arts, a temporary deviation from the mean selected distribution rate occurs as a nonconformity such as a rock  86  or other debris is passed from the hopper  46 . 
     Referring now to FIGS. 9A and 9B, additional aspects of the present invention are illustrated. As discussed herein, an important aspect of the present invention is the provision of a seamless conveyer belt  54 . During routine maintenance or belt  54  replacement, it may be necessary to remove the belt  54  from the roller assemblies  58 ,  60 . To facilitate removal of the continuous belt  54 , a portion  24  of the frame  12  and hopper assembly  46  may be shifted with respect to the frame  12  and pivoted about hopper pivot points  49  as illustrated in FIG.  9 A. Access to the belt  54  may then be gained by elevating a portion of the belt  54  and roller assemblies  58 ,  60  away from the frame  12  as illustrated in FIG.  9 B. The distance between the roller assemblies  58 ,  60  may be decreased to facilitate removal of the belt  54 . Replacement of the belt  54  may be made by placing a new belt  54  around the roller assemblies  58 ,  60 , adjusting the distance between the rollers  58 ,  60 , lowering the belt  54  and roller assemblies  58 ,  60  back onto the frame  12 , and then re-shifting the hopper and frame portion  24  back into operating position. 
     Referring now to FIG. 10, one preferred embodiment of the hydraulic circuit of the top dressing device  10  is disclosed as numeral  130 . Hydraulic circuit  130  is substantially a closed-loop hydraulic system including the pair of wheel driven pumps  32 , the brush assembly motor  72 , the conveyer belt motor  64 , a charge pump assembly  132 , a reservoir tank  134 , a filter  136 , and a multi-function control block  140  having a plurality of ports. The wheel driven pumps  32  are fluidically coupled in parallel between a pump input port  142  and a pump output port  144 . Brush assembly motor  72  and conveyer belt motor  64  are fluidically coupled in series between motor inlet port  146  and motor outlet port  148  of the control block  140 . Charge pump assembly  132  is fluidically coupled between charge pump inlet port  150  and charge pump outlet port  152  of the control block  140 . Charge pump assembly  132  is additionally fluidically coupled to the reservoir  134 . The charge pump assembly  132  includes a mechanically coupled motor and pump assembly for maintaining a fluid charge at the wheel driven pump  32  inlets during operation. Preferably, the motor and pump of the charge pump assembly  132  have capacities of approximately 0.813 and 0.232 cubic inches per revolution, respectively. Importantly, at rest no fluid pressure is developed by the charge pump  132 . Hydraulic fluid from the reservoir is added to the circuit  130  by the pump section of the charge pump assembly  132  in a predetermined ratio (from between 10 to 40%) to make up for fluid loss in the circuit  130 , e.g., motor  72 ,  64  drains, etc. Additionally, the charge pump assembly aids in cooling the closed loop circuit  130  by introducing relatively cool reservoir fluid to the circuit  130 . Filter  136  is coupled to the control block  140  between filter inlet port  156  and filter outlet port  158 . Reservoir  134  is coupled to the control block  140  at reservoir outlet port  160 . 
     The multi-function control block  140  includes a variety of mechanical and electromechanical components, including a normally-open brake solenoid valve  170 , a normally-open motor solenoid valve  172 , a high pressure relief valve  174 , a low pressure relief valve  176 , and check valves  178 ,  180 ,  182 ,  184 . During non-operational intra-site transport of the top dresser  10 , a low load mode may be selected wherein the fluid output from the wheel driven pumps  32  is introduced at pump output port  144 , directed through the pair of normally open solenoid valves  170 ,  172 , directed through the charge pump  132 , through filter  136  and check valve  180 , and returned to the wheel driven pumps  32  via pump input port  142 . During top dressing operation, and upon operator activation of the motor solenoid valve  172  (via the remote switch  38 ), the wheel driven pump  32  output is directed to motor inlet port  146  and through the brush assembly motor  72  and belt motor  64  before returning to the wheel driven pumps  32  as before. Upon activation of the brake solenoid valve  170  by external braking controls (not shown), the wheel driven pump  32  output is directed through the high pressure relief valve  174  before returning to the wheel driven pumps  32 . High pressure relief valve  174  thus imparts a predetermined load upon the wheel driven motors  32  which may be useful to brake the top dresser  10  under some conditions. The preferred ranges of operation of the high and low pressure relief valves  174 ,  176  are approximately 900-1500 psi, and 80 psi, respectively. 
     Control block  140  additionally includes a fill port  186  for introducing fresh fluid into the circuit, as during initial priming, etc. Fill port  186  is coupled to the pump input port  142  and wheel driven pumps  32  through a low pressure check valve  182  which permits air to be released during the refill operation. 
     Control block  140  further includes a check valve  184  for filter bypass, as for example upon filter  136  obstruction. Additionally, check valves  178  and  180  are provided for reverse operation of the top dresser  10 . During reverse motion, wheel pump  32  output is received into the pump input port  142  and recirculated within the control block  140  to the pumps  32  via output port  144 . Check valves  178 ,  180  prevent back-flushing the filter  136  and charge pump assembly  132  during reverse operation. Furthermore, during reverse operation of the top dresser  10  the brush and belt motors  72 ,  64  are inoperable. 
     One preferred embodiment of a hydraulic circuit  130  for the top dresser  10  of the present invention has been illustrated in FIG.  10  and described herein. Modifications and alterations may be appreciated by those skilled in the relevant arts. For example, the charge pump assembly  132  may be replaced with a diaphragm-based pump, a fluid intensifier, an external pump, etc. Furthermore, while embodiments of the present invention described herein references a tow-behind top dresser  10  used in conjunction with a traction vehicle  16 , aspects of the invention may be applicable to other types of top dressers, such as vehicle mounted devices, etc., as appreciated by those skilled in the relevant arts. For example, the gate assembly  84  and gate release device  102  may be adapted for use on other types of particulate distribution devices. Similarly, the hydraulic circuit  130  may be adapted for use on another type of top dressing device. 
     Consequently, as the preferred embodiments of the above top dresser  10  have been described in detail with reference to the attached drawings, it is understood that various changes, modifications, and adaptations may be made without departing from the spirit and scope of the appended claims.