Abstract:
An improved, large capacity, self-propelled, walk-behind power tool, such as a lawn mower, employs a parking brake apparatus which is operative to effectively brake the drive wheels of the tool. The described apparatus is activated by a foot pedal and employs locking fingers having a cooperating lost motion coupling which relieves having to maintain close tolerances for the apparatus during manufacture.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to self-propelled, walk-behind power tools, such as lawn mowers, snow blowers or power sweepers, or like equipment. More particularly, the invention relates to a parking brake organization, especially of the foot operated type, utilizable in equipment in which each drive wheel of a power tool is individually braked. 
     2. Description of the Related Art 
     Although the present invention has utility in walk-behind snow blowers, power sweepers, or the like, the most common utilization of the invention is anticipated for lawn mowing equipment of the concerned type, and particularly, in large capacity, commercial walk-behind mowers. Consequently, except where otherwise expressly stated, the description herein is directed to walk-behind lawn mowing equipment, particularly commercial-type lawn mowers. 
     Commercial-type, self-propelled, walk-behind lawn mowers commonly have a power deck containing two driven wheels and handle bars mounting the operating handles for the various mower control elements. The mower-or tool-deck, which connects with the power deck, carries idler or caster wheels to support and balance it. Each drive wheel is independently operated and includes independent brake means dedicated to each drive wheel. Desirably, parking brake means are also provided to simultaneously lock the operating members for the brakes for both drive wheels when the mower is to be maintained in a prolonged stationary position. 
     Parking brakes for power tools of the concerned type are well known. Such apparatus is shown and described in U.S. Pat. No. 4,558,558 to H. F. Homer, Jr. et al. and U.S. Pat. No. 5,692,366 to T. D. Hardesty. The parking brake apparatus disclosed in these patents both suffer from the disadvantage that the elements operative to simultaneously hold both wheel brakes in a locked condition are located on the handle bars, or on one or more of the control elements carried by the handle bars. The disposition of parking brake operating apparatus on the handle bars of the mower adds further congestion to an already congested region of the mower and renders the parking brake operating apparatus, as well as other mower operation control elements disposed on or about the handle bars, difficult or inconvenient to access. 
     It is to the amelioration of this problem, therefore, to which the present invention is directed. 
     SUMMARY OF THE INVENTION 
     The present invention provides a self-propelled, walk-behind lawn mower containing foot-operated parking brake apparatus operative to simultaneously lock both of a pair of independently operated wheel brakes by depressing a foot pedal which is positioned remotely from the collection of mower operating controls disposed on the handle bars to a position that is readily accessible by the operator&#39;s foot. 
     Accordingly, there is provided by the present invention a self-propelled, walk-behind power tool comprising a bed; a power source and a power train drivingly connecting each drive wheel to the power source; a brake operatively associated with each drive wheel; a brake operator including a lever secured for pivotal movement to the bed and being effective to activate each brake to a braked condition with respect to the associated wheel when the lever is pivoted in one direction, and to a released condition when the lever is pivoted in an opposite direction; and parking brake means for securing the levers for both of the drive wheels in a braked condition, including pawls attached to each lever, an operating shaft journalled to the bed for rotational movement, an activating pedal fixed to the operating shaft for rotating the shaft, a pair of locking fingers containing locking teeth engageable with the pawls and disposed at axially spaced locations along the operating shaft in proximity to the respective pawls, at least one of the locking fingers being angularly displaceable on the operating shaft, and resilient means connecting at least one locking finger to said operating shaft. 
     Preferably, the resilient means that connects the one locking finger to the operating shaft comprises a torsion spring, the opposite ends of which operatively engage such locking finger and the operating shaft, respectively. In the preferred embodiment, one of the pair of locking fingers is fixed to the operating shaft for angular movement therewith. The other locking finger is movable with respect to the operating shaft, being operatively connected thereto by the torsion spring. 
     Moreover, in the disclosed form of the invention, in order to reduce the demands for close manufacturing tolerances in the production of the device, the fixed locking finger is angularly displaced from alignment with the movable locking finger by an amount enabling the movable locking finger to engage its associated locking pawl prior to engagement occurring between the fixed locking finger and its pawl. 
     It is accordingly a principle object of the present invention to provide a lawn mower of the concerned type in which the operating controls are free of congestion and easily accessible by the machine operator. 
     It is a further object of the invention to provide a parking brake apparatus for such lawn mower which is compact, structurally simple and inexpensive to produce, yet effective to simultaneously lock both of a pair of independently operated mower drive wheels. 
     For a better understanding of the invention, its operating advantages and the specific objectives obtained by its use, reference should be made to the accompanying drawings and description which relate to a preferred embodiment thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front perspective view of a self-propelled, walk-behind form of lawn mower incorporating the present invention; 
     FIG. 2 is a rear perspective view of the lawn mower of FIG. 1; 
     FIG. 3 is a side elevational view, partly in section, of the lawn mower illustrated in FIG. 1; 
     FIG. 4 is a partial side elevational view of the handle bar and control-operating handles mounted thereon employed on the mower of FIG. 1; 
     FIG. 5 is a partial perspective view illustrating in greater detail the control elements and the controlled element shown in FIG. 4; 
     FIG. 6 is another partial perspective view of the control elements and the elements controlled thereby shown in FIG. 4; 
     FIG. 7 is a view taken along line  7 — 7  of FIG. 4; 
     FIG. 8 is a plan view of the belt and pulley system employed for operating the drive wheels of the present invention; 
     FIG. 9 is a partial perspective view of the power deck with drive levers and parking brake operator mounted thereon; 
     FIG. 10 is a rear view of the power deck and drive levers of FIG. 9; 
     FIG. 11 is a partial elevational view with portions removed taken along line  11 — 11  of FIG. 8; 
     FIG. 12 is a perspective view of the parking brake operator elements of the present invention; 
     FIG. 13 is a schematic view illustrating parking brake operator elements in various positions; 
     FIG. 14 is a partial perspective view of the operating handle and presence lever for forward operation of the drive wheel on the right side of the lawn mower shown in FIG. 1; 
     FIG. 15 is a view similar to FIG. 13 showing the operating handle and presence lever for reverse operation of the drive wheel on the right side of the lawn mower shown in FIG. 1; 
     FIG. 16 is a schematic representation of the control circuitry for the lawn mower of the present invention; 
     FIG. 17 is a partial perspective view of the blade brake and operating elements thereof for the lawn mower of the present invention; and 
     FIG. 18 is a more detailed partial perspective view of the blade brake and operating elements thereof shown in FIG.  16 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Although the present invention has application to power tools of various forms, such as snow blowers, power sweepers, or the like, the drawing figures illustrate an embodiment of the invention in which the operation element of the power tool is a lawn mower, particularly one employing multiple rotary blades as is common in large capacity, commercial forms of lawn mowing equipment. Also, although the disclosed lawn mower is described as being a “walk-behind” lawn mower, the concerned invention is equally applicable to power equipment attaching a “sulky” or a platform on which the operator may ride. 
     The described lawn mower  10 , as best shown in FIGS. 1-3, contains a power deck  12  and a tool-or mowing-deck  14 . Desirably, the mowing deck  14  is detachably connected to the power deck  12  to permit substituting for the mowing deck, either a snow blowing apparatus or a power sweeping apparatus, neither of which is shown herein. 
     The power deck  12  contains a bed  16  defined by a generally rectangular sheet metal plate  18  having downturned flanges  20 ,  22  and  24  with flanges  20  and  22  being disposed along the laterally spaced sides of the bed, and flange  24  extending between, and interconnecting, the side flanges at the rear of the bed. An engine  26  is mounted on the upper surface of the bed  16  wherein a through-opening  28  is provided to accommodate passage of the engine drive shaft  30  to the underside of the bed plate  18 . An inverted U-shaped bracket  32  has its down-turned legs  32   a  and  32   b  secured to the rear end of the bed  16  and its upwardly disposed platform portion mounting a fuel tank  34 . 
     A pair of laterally spaced drive wheels, including left wheel  36  and right wheel  38 , are disposed on opposite sides of the bed  16  in a manner hereinafter more fully described. Also, a pair of laterally spaced support arms  40  extend longitudinally forward from the bed  16  for attaching the mowing deck  14 . The support arms  40  are fixedly secured at their respective rear ends to the bed and at their forward ends each mount left and right caster wheels  42  and  44 , respectively, which are journalled for free rotation about a vertical axis by associated support shaft housings  460 . As shown best in FIG. 2, the mowing deck  14  is mounted via laterally spaced brackets  448  carrying pivot pins  450  which pivotally engage the respective support arms  40  adjacent the forward ends thereof. A height adjusting mechanism  452  secures the rear end of the mowing deck  14  in a manner which permits height adjustment of the mowing deck. 
     As shown in FIGS. 2 and 3, a handle bar  56  having a pair of left and right depending arms  58  and  60 , respectively, is fixedly secured to the downturned legs of the bracket  32 . A panel plate  62 , that is substantially coextensive with the space along the handle bar  56  between the arms  58  and  60  provides access to control elements, as hereinafter are more fully described. 
     Drive Controls 
     With particular reference to FIGS. 3 to  11  of the drawings, lawn mower control apparatus is shown for controllably operating the left and right drive wheels  36  and  38 . The control apparatus includes individual left and right gear-operated transmissions  64  and  66 , respectively. The transmissions are mutually spaced laterally with respect to each other and each has a horizontally extending output shaft (not shown) extending in opposite directions away from each other with each output shaft being adapted to mount a hub of one of the drive wheels  36 ,  38 . The transmissions are structurally interconnected on their respective facing ends by means of appropriate connecting structure (not shown) and are fixedly secured to the bed  16  of the power deck  12  by means of connectors (not shown) that attach posts which surround an output shaft bearing bushing  72  to laterally extending support ears  74  fixedly secured to the respective side flanges  20  and  22  of the power deck bed  16 . Power input to each transmission  64 ,  66  is effected by a belt-driven input pulley, indicated as  76  on the left transmission  64  and as  78  on the right transmission  66 . Each pulley  76  and  78  is fixed to and rotatably drives input shafts on the respective transmissions  64 ,  68  and extends substantially parallel to the engine drive shaft  30 . 
     As indicated in FIGS. 4,  5 ,  7  and  8  of the drawings, the engine drive shaft  30 , which rotates about a vertical axis, mounts a pair of vertically spaced pulleys  80 ,  82 , about the respective ones of which the drive belts  84 ,  86  extend. Drive belt  84  extends between the uppermost pulley  80  on the engine drive shaft  30  and the pulley  76  on the input shaft to the left transmission  64 . Drive belt  86  extends between the next lower pulley  82  on the engine drive shaft  30  and the pulley  78  on the input shaft to the right transmission  66 . As shown, the input pulley  76  on the left transmission  64  is disposed slightly higher than pulley  78  on the right transmission and substantially level with the pulley  80  on the engine drive shaft  30 . Similarly, the input pulley  78  on the right transmission  66  is disposed substantially level with the pulley  82  on the engine drive shaft whereby the drive belts  84  and  86  each operate in substantially level, horizontal planes. 
     A third pulley, termed “the power take-off (PTO) pulley,”  88  is disposed at the lower end of the engine drive shaft  30  and is engaged by a drive belt  90  employed to rotatably drive the mower blades, as described hereinafter. 
     Belt guards, in the form of rod members  91  attached at one of their ends to the bed  16 , have offset portions positioned closely adjacent the various belts and serve to prevent the respective belts from becoming dislodged from the pulleys which they engage. 
     Power input to the respective drive wheel transmissions is individually controllable by means of clutch elements  92 ,  94  which are each in the form of idler pulleys  96 ,  98  that rotate on one end of pivotable lever arms  100 ,  102 , respectively, whose opposite ends are pivotally secured to the undersurface of the metal bed plate  18 . As shown best in FIG. 7, the lever arms  100 ,  102  which carry the respective idler pulleys  96 ,  98  are each disposed within the space surrounded by the drive belt with which each is associated. Return springs  129  which have one end connected to the bed  16  and the other end connecting each lever arm  100 ,  102  serve to normally bias the idler pulleys  96 ,  98  away from their respective drive belts  84 ,  86 . Also, appropriate limit stops (not shown) extend from the bed plate  18  and serve to limit the angular displacements of the lever arms  100 ,  102  when they are pulled into disengagement by the return springs  129 . 
     Each of the wheel drive transmissions  64  and  66  is a multi-speed geared transmission which produces discrete selected speeds that the panel plate  62  indicates by notches  104  as best shown in FIG.  5 . and include four forward speeds, a reverse speed and a neutral position. A tandem controlled transmission shifting device  105  (FIG. 8) is operative to jointly change the gear of the respective transmissions  64 ,  66 . Geared transmissions, suitable for use in the practice of the invention, are those made by Dana Corp. under Model No. 4360-102. 
     Separate control members operate the clutch elements in order to vary torque transmission between the output of the engine drive shaft  30  and the input to the respective left and right drive transmissions  64 ,  66 . Thus, as shown in the drawings, the bracket  32  on the power deck  12  mounts a support shaft  106  which extends between, and is fixed at its ends, to the respective legs  32   a  and  32   b  of the bracket. Drive levers  108  and  110  having the general shape of an inverted J and disposed at axially spaced locations along the shaft  106  contain clearance openings in the legs of the levers which enable the levers to undergo controlled pivoted movement about the shaft. Spacers  112  serve to separate the drive levers  108 ,  110  from the respective legs  32   a,    32   b  of the bracket  32 . Each of the drive levers  108 ,  110  is independently operated by a respective one of a pair of control handles  114 ,  116  which are disposed for pivotal movement on the handle bar  56  and that contain transversely extending upper portions to facilitate manual manipulation by the machine operator. A connecting rod  118  extends between and connects the respective control handles  114 ,  116  to each drive lever  108 ,  110 . Axial adjustment of the respective connecting rods with respect to their associated drive lever can be effected by a turnbuckle  120  which connects an upper portion  118   a  to a lower portion  118   b  of each connecting rod. 
     Each drive lever  108 ,  110  attaches at a depending leg portion a drive spring  122  which extends forwardly from the drive lever and is generally axially stiff. The springs  122  have at one end a hook  124  that engages an opening  126  in the depending leg of the drive lever  108  and  110 . The other end of each spring  122  contains an elongated loop  125  forming a lost motion space and that, with regard to the left idler pulley  96 , engages a pin  127  which depends from the underside of the lever arm  100 . With regard to the right idler pulley  98 , and in order to accommodate the unequal vertical spacing between the drive belts  84  and  86 , the looped end  125  of the associated spring  122  engages the lower end of bent pin  128  whose upper end is fixed, as by means of welding, or the like, to the edge of the right idler pulley lever arm  102 . 
     Thus, operation of the mower in the forward direction involves, first, the transmissions  64  and  66  associated with the respective wheels  36  and  38  being placed by the operator in a selected drive range, as determined by placement of the shift lever  130  in an appropriate notch  104  in the panel plate  62 . To propel the mower straight forwardly both upper control handles  114   a  and  116   a  are simultaneously moved forwardly whereupon the drive levers  108  and  110  are pivoted about the support shaft  106  in a direction to extend the drive springs  122  rearwardly which causes the lever arms  100  and  102  carrying the idler pulleys  96  and  99  to be controllably urged into engagement with the respective drive belts  84  and  86  thereby adjusting the tension of the respective drive belts about the pulleys they engage. Such adjustment alters the torque transmission from the engine drive shaft  30  to the left and right transmissions  64  and  66 , respectively, within the selected gear range. To steer the mower  10 , the operator need only push or pull one control handle with respect to the other whereupon the driving force to one drive wheel with respect to the other is altered thereby causing the course of the machine to be altered. 
     Reverse propulsion of the mower  10  is accomplished by first moving the shift lever  130  to the reverse position in the notches  104 . Then, the lower control levers  114   b  and  116   b  of the control handles  114  and  116  are pulled rearwardly. This rearward motion of the lower control handles  114   b  and  116   b  has the same effect as the forward motion of the upper control handles  114   a  and  116   a.  The mower  10  may be steered in reverse in the same manner as the forward driving. 
     Braking of the respective drive wheels  36  and  38  in order to stop forward movement of the machine, or to augment its turning movements, is effected by the operator pivotally moving one or the other or both of the control handles  114  and  116  in a direction opposite to that required for effecting rotation of the drive wheels  36 ,  38  for forward movement. Thus, to brake the left drive wheel  36 , for example, the control handle  114  which controls operation of the left drive wheel is pivoted, either by pulling its upper control handle  114   a  backwardly or by pushing its lower control handle  114   b  forwardly. By imparting such movement to the control handle  114 , the connecting rod  118  which interconnects the left control handle  114  with the left drive lever  108  causes the drive lever  108  to rotate in a clockwise direction, as viewed in FIG. 11, whereupon the left brake lever  134  which connects to the drive lever  108  via connecting link  135  is pivoted in a clockwise direction about pivot pin  136  to cause brake band  138  whose ends connect with the brake lever via pin connectors  140  to constrict the brake pad  142  about the brake drum  144  on the wheel. Note that the brake drum  144  for the left wheel  36  has been omitted for clarity and that FIG. 11 shows only the brake drum  144  that is connected to the right wheel  38 . 
     The connecting link  135  includes an elongated loop  135   a  that forms a lost motion coupling with the drive levers  108  and  110 . This loop  135   a  allows the drive levers  108  and  110  to rotate counterclockwise (as viewed in FIG. 11) to engage the idler pulleys  96  and  98  with their respective drive belts  84  and  86  without imparting further motion onto the brake levers  134  which would cause further separation of the brake bands  138  from the brake drums  144 . 
     The simultaneous braking of both drive wheels  36  and  38  is effected by performing the above-described operation simultaneously on both control handles  114  and  116 . Alternatively, in order to augment turning of the machine, one of the drive wheels can be substantially fully, or only partially, braked while the other drive wheel continues to be driven forwardly so as to effect a tight turn. 
     Safety Cut-Off System 
     The safety cut-off system in accordance with the instant invention will be described in connection with the figures set forth below. 
     FIGS. 1-6 illustrate the overall view of the mower including the arrangement of the handle bar controls. As illustrated in FIGS. 4-6, left forward presence lever  201  and right forward presence lever  202  are disposed near left upper control handle  114   a  and right upper control handle  116   a.  Furthermore, the generally elongated shape of left forward presence lever  201  and right forward presence lever  202  generally follows the elongated shape of upper left control handle  114   a  and upper right control handle  116   a.  Furthermore, as noted in FIGS. 5 and 6, the generally elongated shape of reverse presence lever  203  is similar to the elongated shape of the generally horizontal end portion  57  of handle bar  56 . As seen in FIGS. 3 and 4, in profile, left forward presence lever  201 , right forward presence lever  202  and reverse presence lever  203  are generally flat so that they may be easily be grasped together with another bar. Left forward presence lever  201  is easily grasped together with left upper control handle  114   a,  while right forward presence lever  202  is conveniently grasped together with upper right control handle  116   a.  Accordingly, reverse presence lever  203  is conveniently grasped together with horizontal end portion  57  of handle bar  56 , in addition to lower control levers (or reverse control levers)  114   b  and  116   b.    
     FIG. 14 is a partial perspective view isolating right forward presence lever  202  along with its corresponding upper right control handle  116   a  and lower right control handle  116   b.  Specifically, as noted, right forward presence lever  202  generally follows the shape of upper right control handle  116   a.  Accordingly, wherever it is possible to grasp upper right control handle  116   a,  right forward presence lever  202  is also easily grasped at the same time. Because the control handle  116  is pivotable with respect to handle bar  56  through a relative large angle, right forward presence lever  202  is pivotably mounted directly to the right control handle  116 . In fact, since right forward presence lever  202  pivots with respect to right control handle  116 , it is always near to upper right control handle  116   a,  no matter how little or how far upper right control handle  116   a  is pivoted. Normally open, right forward sensor switch  208  is fixed with respect to right control handle  116 . Furthermore, a switch arm  204  extends generally forwardly from right forward presence lever  202  and is fixed with respect thereto. A spring  206  is provided between right forward presence lever  202  and upper right control handle  116   a,  such that right forward presence lever  202  is biased in the OFF state (disengaged state) and thus switch arm  204  is not engaged with plunger  210 . When right forward presence lever  202  is grasped together with upper right control handle  116   a,  that is, the right forward presence lever  202  is now in the ON state (engaged state) switch arm  204  accordingly pivots and presses down plunger  210  of switch  208 . This action causes switch  208  (which is a normally open switch) to be closed and thus to conduct electrical current between contacts  212 , to which control wires are connected. The arrangement of the left forward presence lever with respect to the left control handle  114  is substantially a mirror image of the right forward presence lever  202  and right control handle  116 , illustrated in FIG.  14 . FIG. 3 illustrates left forward presence lever switch  220  which is opposite the right forward presence lever sensor switch  208 . 
     FIG. 15 illustrates the relationship between the reverse presence lever  203  and handle bar  56 . Handle bar  56  is fixed with respect to the mower. Also, as seen in FIGS. 5 and 6, the generally horizontal end portion  57  of handle bar  56  is generally parallel with reverse presence lever  203 . Reverse presence lever  203  is pivoted with respect to handle bar  56 . When reverse presence lever  203  is grasped together with horizontal end portion  57  of handle bar  56 , reverse presence lever  203  is substantially adjacent horizontal end portion  57  of handle bar  56 . A reverse presence lever switch arm  216  extends downwardly from reverse presence lever  203  and is adaptable to engage plunger  222  of reverse presence lever sensor switch  214 . When reverse presence lever  203  is in the OFF state, it is biased away from horizontal end portion  57  of handle bar  56  by spring  218 . Reverse presence lever sensor switch  214  is a normally open switch. Thus, when reverse presence lever  203  is in the OFF state (disengaged state) reverse presence lever sensor switch  214  is maintained open. When the reverse presence lever  203  is grasped together with horizontal end portion  57  of handle bar  56 , switch arm  216  is pivoted to contact plunger  222  and accordingly to close sensor switch  220 . 
     FIG. 16 is a schematic diagram of the control circuit layout for controlling the safety cut-off system in response to the operation of the presence levers and control levers. Reference numeral  240  generally refers to the circuit for controlling the safety cut-off system. Circuit  240  is connected to connection block  236  with labeled connections B-F. Connection block  236  is in turn connected to switching module  238 , which is available from Alphabet Wire Harness as Model No. 135331. Of course, module  238  may be any type of a switching module with relays, switches, electronic switches, a programmed logic array, or any other appropriate switching device. 
     Engine magneto  234  is connected to key switch  230  and is also connected to contact B. Key switch  230  is normally open when the engine is running. The opposite side of key switch  230  is connected to ground, thus when key switch  230  is closed, the engine magneto is grounded and the mower is prevented from running. On the side of key switch  230 , opposite the engine magneto, key switch  230  is also connected to contact E. An hour meter  232  is connected between contact points B and E. Contact point C is connected to a front side of reverse gear sensor switch  226  (normally closed) and to the front side of reverse presence lever sensor switch  214 . The back side of reverse gear sensor switch  226  is connected to a first lead of left forward presence lever sensor switch  220  and in parallel to a first lead of right forward presence lever sensor switch  208 . The first lead of left forward presence lever sensor  220  is also connected to a first lead of power take-off sensor switch  228  (normally closed). The second lead of power take-off sensor switch  228  is connected to contact D. The second lead of left forward presence lever sensor switch  220  is connected to contact F. The second lead of right forward presence lever sensor switch  208  is connected to a second lead of reverse presence lever sensor switch  214  and to contact F. 
     During operation, in its most basic sense, one or both of the forward presence levers  201 ,  202  are pushed forward (into the ON state) when the lawn mower is neutral or forward gear, and while pushing forward on the upper control handles  114 ,  116 . When the lawn mower is in reverse gear, the reverse presence lever  203  is depressed onto the horizontal end portion  57  of handle bar  56 , while pulling backward on lower control handles  114   b,    116   b.  Module  238  functions to connect contact E (at ground potential) to contact B to provide a ground level signal to the engine magneto and thus prevent the motor from running. When contact C is connected to contact D or F, then the connection between contact B and contact E is broken, and thus contact B is no longer at ground potential, therefore enabling the motor to run. 
     As noted, reverse gear sensor switch  226  is normally closed. This means that when reverse is gear engaged, switch  226  becomes open. When switch  226  becomes open, the only way for contact C to conduct to contact F is through reverse presence lever sensor switch  214 . In order words, the only way to prevent cutting-off of the motor is to engage (put into the ON state) the rear presence lever  203 . Thus, if the gear shift is in the reverse gear, irrespective of the status of right forward presence lever switch  208 , left forward presence lever switch  220  and power take-off sensor switch  228 , the reverse presence lever sensor switch  214  must be closed in order to prevent a cut-off of the motor. 
     When the lawn mower is in neutral or a forward gear, reverse gear sensor switch  226  is closed. Accordingly, any one of reverse presence lever sensor switch  215 , left forward sensor switch  220 , or right forward sensor switch  208  may be closed (either of the two forward presence levers or the reverse presence levers in the ON state) in order to prevent contact B (and thus the engine magneto) from being grounded. 
     Power take-off lever sensor switch  228  is normally closed. That is, when the power take-off unit is engaged, the switch is open, and when the power take-off unit is disengaged then switch  228  is closed. 
     A clear view of how the schematic diagram of FIG. 16 works can be seen with reference to the following table A. 
     
       
         
               
               
               
               
               
               
               
             
           
               
                 TABLE A 
               
               
                   
               
               
                 No. 
                 Gear 
                 PTO 
                 Right Fwd PL 
                 Left Fwd PL 
                 Rev PL 
                 Engine 
               
               
                   
               
             
             
               
                 1 
                 N-4 
                 ON 
                 OFF 
                 OFF 
                 OFF 
                 OFF 
               
               
                 2 
                 N-4 
                 ON 
                 ON (OFF) 
                 OFF (ON) 
                 OFF (ON) 
                 ON 
               
               
                 3 
                 N-4 
                 OFF 
                 OFF (ON) 
                 OFF (ON) 
                 OFF (ON) 
                 ON 
               
               
                 4 
                 R 
                 OFF 
                 OFF 
                 OFF 
                 OFF 
                 OFF 
               
               
                 5 
                 R 
                 OFF 
                 ON (OFF) 
                 OFF (ON) 
                 OFF 
                 OFF 
               
               
                 6 
                 R 
                 OFF 
                 OFF (ON) 
                 OFF (ON) 
                 ON 
                 ON 
               
               
                 7 
                 R 
                 ON 
                 OFF 
                 OFF 
                 OFF 
                 OFF 
               
               
                 8 
                 R 
                 ON 
                 ON (OFF) 
                 OFF (ON) 
                 OFF 
                 OFF 
               
               
                 9 
                 R 
                 ON 
                 OFF 
                 OFF 
                 ON 
                 ON 
               
               
                   
               
             
          
         
       
     
     As can be seen from Table A, the different status of the right forward presence lever, the left forward presence lever and the reverse presence lever affect the engine depending on which gear is selected and whether the power take-off unit (PTO) is engaged (ON) or disengaged (OFF). Specifically, items 1-3 illustrate the situation in which the gear selector is in neutral or forward gears  1 - 4 . In this situation, if the PTO is on, the engine will be prevented from running if neither the right forward presence lever  202 , the left forward presence lever  201  nor the reverse presence lever  203  are in the ON position. Item 2 indicates that if one of the three presence levers is ON, then the motor or engine will not be prevented from running. Item 3 indicates that if the PTO is OFF and neutral or a forward gear is selected, then the position of the presence lever does not matter and the engine is not prevented from running. 
     Items 4-9 indicate the situation in which the lawn mower is in reverse gear. As can be seen in items 4-9, whether the PTO is ON or OFF, the only condition which will allow the motor to be ON is when the reverse presence lever  203  is also in the ON state. 
     Parking Brake 
     The disclosed mower includes a parking brake assembly identified generally by reference numeral  300  and described with particular reference to FIGS. 9,  11 ,  12  and  13  of the drawings. The parking brake apparatus for the respective drive wheels  36  and  38 , includes the drive levers  108 ,  110 , which are pivotally supported by support shaft  106  and which operate to constrict the brake bands  138  about the hubs of the respective drive wheels through activation of brake levers  134  by the respective drive levers and connecting links  135  which connect the brake levers to the drive levers. 
     The parking brake assembly  300  includes an operating shaft  302  which extends laterally across the rear of the bed  16  of the power deck  12 , with the opposite ends of the shaft being mounted for rotation in openings  146  formed in the side flanges  20  of the bed plate  18 . A pedal arm  304  having a foot pedal  306  attached at its free end is fixedly secured to the operating shaft  302 , whereby the operating shaft is caused, when activated, to rotate in a counter-clockwise direction, as viewed from the right hand end in FIG.  12 . 
     As shown in the drawing figures, each drive lever  108 ,  110  has a pawl  308  in the form of an inclined U-shaped projection extending from a side surface of a depending leg of the drive lever. The operating shaft  302  contains a pair of locking fingers  310  and  312 , each of which contains an upwardly facing side edge  314  having an arcuately formed portion adjacent the free end and having locking teeth  316  thereon adapted to engage the pawls  308 . In order to facilitate engagement of the pawls  308  on the drive levers  108 ,  110  with the locking teeth  316  on the locking fingers  310 ,  312 , the free ends of the teeth are arcuately formed. Also, as shown in FIG. 13 which illustrates a drive lever  108 ,  110  in both of its extreme positions of engagement with the locking levers, the inclination of the pawls  308  and the disposition of the teeth  316  along the locking finger edge  314  is such as to ensure a full surface engagement of each pawl with the locking finger teeth wherein the engagement force vectors are substantially normal to the engaging surface on the pawl, as indicated by direction lines  318  and  320 . 
     According to the invention, the locking finger  310  is fixed, as by means of welding, to the operating shaft  302  so as to rotate with the shaft. A return spring  321 , which is connected at one end to a hole  322  in the locking finger  310  and whose other end is fixed with respect to the bed  16 , biases the locking finger  310 , and consequently the shaft  302 , in a direction away from the drive levers. This bias is overcome when the foot pedal  306  is depressed. Locking finger  312  is connected to the operating shaft  302  in a manner as to permit a restricted amount of relative movement with respect to the shaft in order to provide a lost motion function between the locking finger and the shaft. As shown, the locking finger  312  has a clearance hole  324  through which the operating shaft  302  loosely passes. A pair of radially extending pins  326  and  328  are fixed to the shaft at axially spaced locations therealong. Pin  326  is positioned closely adjacent the right side of locking finger  312 , as viewed in FIG. 12, and pin  328  is located at a position remote from the left side of the locking finger. A torsion spring  330  surrounds the operating shaft  302  between the left side of locking finger  312  and the radial pin  328 . A tang  332  on the right end of the torsion spring  330  attaches the locking finger  312  via a connecting hole  334  therein. The left end of the torsion spring  330  contains an arm (not shown) which bears against radial pin  328 . During assembly of the torsion spring onto the shaft, the spring is pre-loaded in a tightening direction so as to bias the movable locking finger  312  upwardly toward the adjacent pawl  308 , with such upward movement being limited by engagement of the tang  332  with the radial pin  326 . 
     As is evident from consideration of FIG. 12, the locking fingers  310  and  312  are not angularly aligned about the operating shaft  302 . Instead, the movable locking finger  312  is displaced angularly upwardly with respect to the fixed locking finger  310  so as to engage the pawl  308  on drive lever  108  prior to engagement by the fixed locking finger  310  with the pawl  308  on drive lever  110 . As a result of this construction, depression of the foot pedal  306  by the machine operator causes, first, the teeth  316  on the movable locking finger  312  to engage the pawl  308  on the drive lever  108  in order to lock the drive lever, and concomitantly, the associated brake lever  134  in their counter-clockwise positions to hold the brake band  138  constricted about the brake drum  144  of the left drive wheel. Immediately thereafter, the fixed locking finger  310  is brought into engagement with the pawl  308  on drive lever  110  so as to secure the drive lever in its braked condition, limited continued rotation of the operating shaft  302  being permitted due to the lost motion function effected by the coupling of locking finger  312  to the operating shaft  302  through the torsion spring  330 . 
     The operation of the described parking brake assembly  300  is as follows. When the drive control handles  114  and  116  (FIG. 6) that connect with drive levers  108  and  110 , respectively, are pulled backward by the machine operator, the brake bands  138  constrict brake pads  142  about the brake drums  144  to apply a braking force to the respective drive wheels  36 ,  38 . The residual forces developed in the brake bands  138  bias the control handles  114  and  116  to a neutral position on the handle bar  56 , which position is intermediate their “drive” position and their “brake” position. Coincident with this, drive levers  108 ,  110  and their associated brake levers  134  tend to move in a counterclockwise direction as viewed in FIG.  11 . 
     The parking brake function is initiated by the machine operator depressing the foot pedal  306  with the wheel brakes being manually applied and the control handles  114 ,  116  being held by the operator in their “brake on” or rearward position. Consequently, operating shaft  302  is rotated counter-clockwise to move the locking fingers  310 ,  312  toward the pawls  308  on the respective drive levers  108 ,  110  whereupon locking teeth  316  on the movable locking finger  312 , which is upwardly biased out of alignment with fixed locking finger  310 , are caused to engage the pawl  308  on the drive lever  110 . With the torsion spring  330  providing a lost motion coupling between the movable locking finger  312  and the operating shaft  302 , the shaft continues to rotate until the locking teeth  316  on the locking finger  310  engage the pawl  308  on drive lever  110 . 
     A force perpendicular to the end face of the pawl  308  results when the teeth  316  engage the pawl  308 . This force is the result of the inclination of the pawl  308  and the bias on the drive lever  108 ,  110  to rotate clockwise. The direction of this force is represented in FIG. 13 by lines  318  and  320  for the two positions illustrated. 
     The force generated between the teeth  316  and the pawls  308  is directed over the pivot (i.e., the center of the operating shaft  302 ) of the locking fingers  310  and  312 . This force tends to rotate the locking fingers  310  and  312  upwardly (counterclockwise). However, the pawls  308  (which are attached to the drive levers  108  and  110 ) tend to rotate clockwise to the “neutral” drive lever position of the drive levers  108  and  110 . Thus, each engaged member has a force applied to it that biases each member further into engagement. 
     This perpendicular force creates a frictional force between the engaged tooth  316  and the pawl  308 . The frictional force is perpendicular to the force along line  318  or  320 . The frictional force counteracts the force of the return spring  321  attached to the locking finger  310 . The interaction of the perpendicular force, the friction force and the return spring force creates a self-locking relationship between the pawls  308  and the locking fingers  310  and  312 . Therefore, the parking brake assembly remains engaged. 
     For releasing the parking brake, the machine operator pulls the control handles  114 ,  116  rearwardly. Such action causes movement of the drive levers  108 ,  110  in a clockwise direction which results in the pawls  308  being removed from engagement with the locking teeth  316  on locking fingers  310 ,  312 . When this occurs, the force resisting the return spring  321  is removed and the fixed locking finger  310  falls away from its associated pawl  308  thereby moving with it the operating shaft  302  and the movable locking finger  312  whereupon the parking brake becomes fully disengaged. 
     From the foregoing, it is evident that the described parking brake organization is of simple, inexpensive construction, yet is effective for its intended purpose and, moreover, as compared with comparable devices of the prior art, permits location of the parking actuator in an uncongested, easily accessible location on the mower. 
     Blade Brake Assembly 
     The blade brake assembly in accordance to the instant invention is operated when the power take-off unit is disengaged. Specifically (as seen in FIG.  17 ), the power take-off unit includes a power take-off (PTO) drive pulley  88  driven by the motor, and PTO drive belt  90  driven by the PTO drive pulley  88 . Mower deck drive pulley  428  is engaged with PTO drive belt  90  and is driven by it. Mower deck drive pulley  428  is attached to and co-axial with shaft  430  which drives the center mower blade. A mower deck drive belt  436  is threaded around center mower deck pulley  444 , immediately beneath mower deck drive pulley  428  and also supported on shaft  430 . The mower deck drive belt  436  is also threaded around right side mower deck pulley  440 , which is supported on shaft  434  which also support the right side mower blade. The mower deck drive belt  436  is furthermore threaded around left side mower deck pulley  442  which is disposed immediately beneath the blade brake assembly  446  and is supported on left side shaft  432  which also supports the left side mower blade. A mower deck tension pulley  438  provides proper tension on mower deck drive belt  436  for driving all three mower blades. PTO idler pulley  414  is inserted in contact with PTO drive belt  90  between PTO drive pulley  88  and mower deck drive pulley  428 . When PTO idler pulley  414  is engaged with PTO drive belt  90  and is biased outwardly, the power take-off unit is engaged and the mower deck drive pulley  428  is driven. When PTO idler pulley  414  is shifted inwardly (as shown in phantom) so that it no longer applies tension on PTO drive belt  90 , the power take-off unit is disengaged. In other words, mower deck drive pulley  428  is not driven. 
     PTO idler pulley  414  is shifted inwardly to disengage the PTO unit. PTO idler pulley  414  is shifted inward in response to PTO control lever  402 , as best seen in FIGS. 6 and 17. PTO control lever  402  is connected by way of upper rod  404  to first arm  406 . First arm  406  is fixed with respect to second arm  408  by way of collar  410 . Collar  410  is supported by and rotates around shaft  106 . Second arm  408  is connected by way of lower rod  412  to a lower mounting fitting  427 . Furthermore, a damping spring  422  is provided on a remote end of lower rod  412 , on the opposite of lower mounting fitting  427  from second arm  408 . An idler pivot  420  fixed to the power deck includes first PTO idler arm  416  and second PTO idler arm  418 . First PTO idler arm  416  extends outwardly from idler pivot  420  and rotatably supports PTO idler pulley  414 . Second PTO idler arm  418  extends outwardly from idler pivot  420  and provides a mounting surface for lower mounting fitting  427  which provides for a pivotal connection with rod  412 . An upper mounting fitting  426  is provided on the upper portion of second PTO idler arm  418 . In response to the movement of rod  412 , second PTO idler arm  418 , and in turn first PTO idler arm  416  pivots about idler pivot  420 , thus causing PTO idler pulley  414  to move inwardly (as shown in phantom) and outwardly with respect to the PTO drive belt  90 . Belt guide  424  is simply provided to prevent PTO drive belt  90  from slipping off of PTO idler pulley  414  as it releases its tension and moves inwardly with respect to the belt. Thus, when PTO idler pulley  414  is shifted inwardly, the PTO unit is disengaged. 
     As illustrated in FIG. 3, the lawn mower having a blade braking system in accordance with the instant invention is adjustable for different cutting heights. Specifically, as seen in FIG. 3, the mower deck  14  is illustrated in its high position. It is also illustrated in its low position  15 , as indicated in phantom. The lawn mower is supported on the ground by drive wheels  36 ,  38  in the rear and by caster wheels  42 ,  44  in the front. Support arms  40  are fixed with respect to the power deck  12 . At the forward end of support arms  40 , the caster wheels  42 ,  44  are supported. A support shaft housing  460  is fixed to the forward end of each support arm  40 , and supports a caster support shaft  458  therein. Support housing  460  is adjustable up and down along the length of caster support shaft  458 , in order to raise and lower support arms  40  with respect to the caster wheel and the ground. Preferably, spacers  480  (see FIG. 2) may be inserted or removed from below each support shaft housing  460  in order to raise or lower it with respect to the associated caster wheel. Mower deck  14  is mounted to support arm  40  by way of a pair of brackets  448  (FIG. 17) which are supported on support arm  40  by way of pivot pin  450  (FIG. 3) being inserted in opening  451  of bracket  448  (FIG.  17 ). While the left side is being described, it should be noted that the right side is similar. 
     As illustrated in FIGS. 3 and 17, a height adjusting mechanism is generally indicated by the arrow  452  and includes a pivot bar  454  which pivots (through angle  453 ) with respect to support arms  40  and has an inwardly extending engaging end  455 . Pivot bar  454  pivots about a pivot portion  451  (see FIG.  17 ). The engaging end  455  supports bracket  456  which is fixed to the top of the lawn mower deck. As seen in FIGS. 2 and 3, a deck height lever  482  is fixed to a forward end of pivot bar  454 . Deck height lever extends upwardly with a remote end easily grasped by an operator. A notched adjustment track  484  is in interlocking engagement with deck height lever  482 , wherein deck height lever  482  is incrementally shiftable with respect to notched adjustment track  484  into one of a number of predetermined positions indicated by a notch in notched adjustment track  484 . Each predetermined position represents a different cutting height. Since deck height lever  482  is fixed to pivot bar  454 , as deck height lever  482  is pivoted, pivot bar  54  pivots or rotates (through angle  453 ) with respect to support arm  40 , and inwardly engaging ends  455  shift downwardly with respect to support arm  40 . Since engaging ends  455  support brackets  456  and thus mower deck  14 , as engaging ends  455  shift downwardly, so do brackets  456  and accordingly mower deck  14 . However, mower deck  14  is pivoted at pivot pin  450  (FIG.  3 ). Thus, the mower deck pivots downwardly and does not remain level with respect to the ground. This causes two concerns. The first concern is maintaining the mower deck and the mower blade in a position substantially parallel to the ground. This is accomplished by adjusting the height of support shaft housing  460  with respect to caster support  458 . Therefore, when the mower deck  14  is adjusting downwardly or upwardly by the height adjusting mechanism  452 , the support shaft housings  460  are also adjusted to compensate. 
     A second concern arising from the pivoting deck is the proper connection of a linkage to the blade brake for braking the mower blades when the PTO unit is disengaged. This solution will be described below. 
     When the PTO is disengaged, then ANSI regulations require the blades to stop moving within specified amount of time. Thus the blade brake should be applied when the lawn mower is shifted into the PTO disengaged state. Accordingly, as illustrated in FIG. 17, actuating rod  462  is connected to second PTO idler arm  418  by way of pivotable upper mounting fitting  426 . Actuating rod  462  extends forwardly from second PTO idler arm  418  to pivot lever  464 . Pivot lever  464  pivots about a center pivot  466  which is fixed to mower deck  14  (illustrated as  14 ′ in FIG.  18 ). Pivot lever  464  (as seen in FIGS. 17 and 18) transfers the longitudinal reciprocating movement of actuating rod  462  indicated by arrow a into the longitudinal reciprocating movement of link member  468  indicated by arrow b. Center pivot  466  and pivot lever  464  are fixed to the mower deck at a point near the mower deck pivot pin  450  which pivots in openings  451  of brackets  448 . As noted in FIG. 18, the forward end of actuating rod  462  has a connecting end  476  extending generally perpendicular to the actuating rod  462 . Connecting end  476  is inserted into an oversize hole  478  such that actuating rod  462  is pivotable in two different angular directions with respect to pivot lever  464 . Actuating rod  462  pivots in a direction generally parallel to the plane of the pivot lever  462  as indicated by arrow c. Furthermore, because of the oversize hole  478  and the connecting end  476  of actuating rod  462 , actuating rod  462  is also pivotable in a direction not parallel to the plane of pivot lever  464 . In fact, actuating rod  462  is pivotable in a direction generally perpendicular to the plane of pivot lever  464  as indicated by arrow f. Link member  468  extends from a pivotal connection with a second end  474  of pivot lever  464  to connect with bard brake  446 . A support ring  470  (FIG. 17) is fixed to the mower deck to support an end of link member  468  nearest the band brake. As link member  468  shifts toward the band brake, the band brake is applied, braking the left mower blade and the other mower blades by way of mower deck drive belt  436 . As illustrated in FIG. 18, it is preferable that the distance between the center pivot  466  and the connection of pivot lever  464  with actuating rod  462  indicated by d 2  is greater than the distance from center pivot  466  to the connection between pivot lever  464  and link member  468  (indicated by d 1 ). Since the pivot lever  464  is located near pivot pin  450  of the mower deck, the pivotability of actuating rod  462  in two different angular directions compensates for the pivoting of the mower deck when raising and lowering the height adjustment. Furthermore, because actuating rod  462  is a long rod and pivoted at pivot lever  464 , any large change in lateral movement of actuating rod  462  at the end nearest the power deck is reduced to a smaller amount near pivot lever  464 . Furthermore, when d 2  is greater than d 1 , any difference in longitudinal motion of actuating rod  462  (between high and low cutting levels) is accordingly reduced in the longitudinal motion of link member  468 . Thus, the pivoting movement of the mower deck when changing cutting height is compensated for without requiring continued adjustment of the blade brake itself, and thus enabling the blade brake to always be in proper alignment, since it is fixed with respect to the location of center pivot  466  and pivot lever  464 . 
     In operation, when the operator moves the PTO control lever  402  to select a disengaged state for the PTO unit, motion is transmitted through tipper rod  404 , first arm  406 , collar  410 , second arm  408 , lower rod  412 , through lower mounting fitting  427  to pivot second PTO idler arm  418  about idler pivot  420 . When idler pivot  420  pivots in the clockwise direction, first idler arm  416  and PTO idler pulley  414 , rotatably attached thereto, are pivoted in turn. As PTO idler pulley  414  is shifted inwardly, the tension on PTO drive belt  90  is removed and power to mower deck drive pulley  428  is removed. As second PTO idler arm  418  moves forwardly, so does actuating rod  462 , because it is pivotally connected to second PTO idler arm by way of pivotable upper mounting fitting  426 . As actuating rod  462  moves forward, pivot lever  464  pivots about center pivot  466  and causes link member  468  to be moved longitudinally toward band brake  446  and thus apply band brake  446  to thereby stop the rotation of the mower blades. 
     When the PTO control lever  402  is returned to the engaged state to engage the PTO unit, each of the above elements operates in the reverse way to release band brake  446  and thus to allow the mower blades to spin freely. 
     Ballast System 
     The ballast system in accordance with the instant invention can best be seen with reference to FIGS. 3-6. Ballast tank  252  is illustrated in these figures. The ballast system in accordance with the instant invention is used with a lawn mower  10  having a power deck  12  and a mowing deck  14 . An engine or motor  26  is positioned on bed  16  of power deck  12  for driving left and right drive wheels  36 ,  38 . Mower deck  14  is attached to and extends forwardly from power deck  12  and is supported at its front end by caster wheels  42 ,  44 . A fuel tank  34  is supported on bracket  32  located at the rear portion of power deck  12 . Depending arms  58 ,  60  extend upwardly and rearwardly from the power deck and are fixed to and supported by bracket  32 . Ballast tank  252  is supported between depending arms  58 ,  60  of the handle bar  56 . As seen most clearly in FIGS. 3 and 4, ballast tank  252  is disposed near the end of handle bar  56 , remote from power deck  12 . FIGS. 3 and 4 illustrate a filler cap  254  or opening the top of ballast tank  252  to fill the interior volume with the desired ballast, whether water, sand or any other appropriate ballast. Draining cap  256  allows the ballast to be easily drained out from ballast tank  252 . 
     As clearly seen in FIG. 3, ballast tank  252 , disposed near an end of handle bar  56 , is located behind the center line of drive wheels  36 ,  38 . In fact, the ballast tank  252  is disposed behind the rearmost portion of drive wheels  36 ,  38 . Furthermore, it should be noted that ballast tank  252  is disposed at least partially behind fuel tank  34 . 
     In operation, the filler cap  254  may simply be removed by the operator and ballast tank  252  may be filled with water, sand or any other appropriate ballast. Cap  254  may then be replaced. The appropriate ballast in ballast tank  252  will change the center of gravity of the lawn mower itself. It will aid to counter balance the mower deck  14  attached on the front of the power deck  12 . This will aid in handling the lawn mower in tight places, or under any other circumstances. Because ballast tank  252  is disposed high up on handle bar  56 , in order words, near the end of handle bar  56 , this arrangement increases the movement arm of any ballast in ballast tank  252 , thus increasing the efficiency of any such ballast. When finished, the user may drain the ballast through drain cap  256 . 
     It should also be noted that although the above description has been set forth with regard to the mower deck  14 , the power deck  12  may also be employed with a snow blower, auxiliary unit, a power sweeper auxiliary unit or many other types of auxiliary units. As an example, the lawn mower deck may have a different weight than the snow blower auxiliary unit or the power sweeper auxiliary unit. Accordingly, because the ballast tank  252  has an interior volume that may accept varying amounts of ballast, the ballast tank  252  may be filled full, or may be partially filled to compensate for different weights of the different auxiliary units, such as the mower deck, the snow blower auxiliary unit and the power sweeper auxiliary unit. 
     It will be appreciated that the power tool drive apparatus described herein, utilizing gear-operated drive transmissions, produces operating characteristics and features which heretofore were unique to equipment employing hydrostatic transmissions for transmitting engine power to the drive wheels. The disclosed arrangement provides a compactness of form which enables all of the components, which define the drive train, to be enclosed by the power deck bed, thus to protect the drive train components against damage occurring from the components contacting tree limbs or other vegetation, or the like. Conversely, by enclosing the drive train components, the machine operator and others who might come in close proximity to the machine are protected against injury caused by contact with moving drive train components. 
     These and other advantages previously attributable to hydrostatic transmissions are effectively obtained from gear-operated transmissions by practice of the invention wherein the clutching function, that is required for the use of gear-operated transmissions, is effected by the engagement of idler wheels on the drive belts, which engagement occurs on belts that transmit drive torque from the engine to the input to the transmission instead of to the output of the transmission as has been the practice of the prior art. As a result, because the clutching function is imposed on drive belts subjected to high speed but low torque, as contrasted with the converse, which prevails with prior art belt driven machines of the concerned type, undue wear caused by belt slippage is avoided. Therefore, the frequency of belt replacement, with its attendant inoperability of the machine, is significantly reduced. 
     Undue stressing of drive belts utilized in the described machine is further reduced by the fact that the idler pulleys are caused to engage the associated belts on the inside surface of the belts, i.e., the same surface as is engaged by the driving and driven pulleys of the system. Thus, compressive stresses are continuously imposed upon the inside belt surface while the outside belt surface is continuously stressed in tension. These continuous stress conditions are contrasted with prior art devices wherein, due to the idler pulley engaging the concerned belts on the side opposite that engaged by the drive and driven pulleys, the belts undergo the alternate imposition of compression and tension stressing which results in increases in belt fatigue and rapid belt wear. 
     Although a specific form of embodiment of the instant invention has been described above and illustrated in the accompanying drawings in order to be more clearly understood, the above description is made by way of example and not as a limitation to the scope of the instant invention. It is contemplated that various modifications apparent to one of ordinary skill in the art could be made without departing from the scope of the invention which is to be determined by the following claims.