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BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a rotary power trowel machine for finishing concrete surfaces and more particularly to a quick adjustment mechanism for the pitch of the blades of a concrete power trowel.  
           [0003]    2. Description of the Prior Art  
           [0004]    Rotary power trowels have been used for many years to level and finish large concrete surfaces. Rotary power trowels include a driven rotatable trowel blade assembly having a plurality of radially extending, generally flat trowel blades which rest directly on the surface being finished. The trowel blades can be pivoted about their radial axis to change the pitch of the blades as required depending upon the characteristics of the concrete surface being finished.  
           [0005]    U.S. Pat. No. 4,232,980 issued Nov. 11, 1980 to the assignee of the present invention discloses a rotary power trowel in which the pitch of the rotatably driven blades can be adjusted by rotating a knob or hand wheel at the upper end of an elongated control handle for the machine. Under certain circumstances, it becomes desirable to quickly change the pitch of the rotary trowel blades in order to obtain the desired finish on the concrete surface. Various efforts have been made to provide a quick adjustment of the pitch of the rotary trowel blades. The following U.S. patents illustrate various assemblies associated with the rotary trowel blades to quickly vary the pitch about their respective radial axes.  
                                                           4,577,993   5,147,146   5,993,109           4,673,311   5,405,216                      
 
           [0006]    While the above patented devices disclose structures for rapid adjustment of the pitch of the rotary trowel blades, these prior structures do not provide a quick adjustment for the blade pitch which achieves the mechanical simplicity and ease of operability obtainable by the structure of the present invention.  
         SUMMARY OF THE INVENTION  
         [0007]    The rotary power trowel of the present invention includes a unique quick adjustment for the blade pitch which enables the blade pitch to be rapidly and effectively adjusted. The unique blade pitch adjustment also quickly and easily locks the adjustment assembly in adjusted position and quickly and easily unlocks the assembly when it is desired to change the blade pitch. The quick adjustment assembly of this invention includes a control lever pivotally mounted on the shaft of the operating handle of the trowel at a position just forwardly of and between the handle bar grips on the operating handle. The control lever includes a trip handle extending upwardly from the control lever to be easily grasped by an operator holding the trowel by the handle bar grips.  
           [0008]    The control lever is associated with a semicircular guide mounted longitudinally on the shaft of the operating handle of the trowel with the center of the semicircular guide coinciding with the pivot axis of the control lever. The trip handle is then operated to lock the control lever in any adjustment position selected around the semicircular guide. The opposite end of the control lever has an actuating rod or link pivotally connected thereto which extends forwardly into connecting engagement with one end of a pivot link also pivotally mounted on the shaft of the operating handle. The other end of the pivot link includes a partial circular segment. The cable connected at one end to the actuating mechanism for moving a swash plate associated with the rotary blades to vary their pitch angle in a well known and conventional manner has its other end wound around the partial circular segment of the pivot link.  
           [0009]    By actuating the trip handle and pulling the control lever rearwardly (towards the handle bar grips), the connecting rod is forced forwardly (away from the handle bar grips) thus rotating the pivot link to cause the cable to move upwardly in the operating handle shaft. This upward movement of the cable depresses the actuating mechanism to move the swash plate downwardly and cause the trowel blade pitch angle to increase. When the control lever is pushed forwardly (away from the handle bar grips), the connecting rod moves rearwardly and the pivot link rotates to relax the tension on the cable. The weight of the trowel then causes the pitch angle to decrease to the extent permitted by the relaxed cable.  
           [0010]    In one embodiment of the invention, the control lever and trip handle include a pivotal locking plate having a slot shaped opening which receives the semicircular guide. The pivotal locking plate locks the control lever to the arcuate upper and lower edges of the semicircular guide to prevent movement of the control lever. The trip handle includes a trigger mechanism that is actuated to move the locking plate out of locking engagement with the arcuate edges of the semicircular guide to enable the trip handle and lever to pivot in order to change the pitch of the blades. The trigger mechanism is preferably associated with the trip handle so that normal movement of the hand of the trowel operator into engagement with the trip handle will actuate the trigger mechanism to release the trip handle and lever from the guide when it is desired to reduce the pitch of the trowel blades by pivoting the locking plate to perpendicular relation to the guide. When the trip handle and control lever are moved in the direction to increase the blade pitch, the locking plate slot edges will move along the guide edges to permit movement of the control lever in the direction to increase the pitch and it is not necessary to operate the trigger mechanism when increasing the blade pitch with it only being necessary to pull the trip handle toward the handle bars of the control handle for the rotary power trowel.  
           [0011]    In a second embodiment of the invention, the semicircular guide has notches on its underneath arcuate surface. The control handle and lever have a spring biased latch mechanism that engages these notches in a desired adjusted position. The latch mechanism is released by a depressable button-like projection in the upper end of the trip handle to release the lever from the guide and enable the control lever to be moved in either direction.  
           [0012]    In both embodiments of the invention, the structural relationships of the operating components is important. The control lever handle is spaced a longer distance from the pivot point of the control lever on the operating handle shaft than the distance between the control lever pivot point and the point of connection with the connecting rod. Similarly, the distance between the point of connection of the connecting rod with the pivotal link is shorter than the radius of the circular segment of the pivot link. These differences in length to the respective pivot points of the control lever and pivot link provide a substantial mechanical advantage. This mechanical advantage enables the control lever to be pivoted in a manner to increase the pitch of the trowel blades even when all of the weight of the trowel is resting on the trowel blades. The weight of the trowel resting on the trowel blades maintains tension on the cable that connects to the swash plate actuating mechanism at all times. The mechanical advantage leverage built into the adjustment mechanism of the present invention allows the operator to increase the pitch of the blades with a minimum of effort. It also enables the operator to effectively control a decrease in the blade pitch by slowly moving the trip handle forwardly to whatever pitch angle is desired, even a zero pitch angle where the rotary blades lie flat on the concrete surface. .  
           [0013]    Accordingly, it is an object of the present invention to provide a quick adjustment mechanism for the pitch of radial blades in a rotary power trowel which can be quickly locked and unlocked to enable the pitch of the blades to be quickly adjusted.  
           [0014]    Another object of the present invention is to provide a quick adjustment mechanism having a mechanical advantage linkage for efficient adjustment of the blade pitch and to reduce the force required to vary the pitch of the blades.  
           [0015]    Still another object of the present invention is to provide a quick adjustment mechanism for the blade pitch of a power trowel incorporating a control lever having a trip handle oriented just forwardly of the handle bars on the operating handle of the trowel and extending above the operating handle for easy access by an operator of the trowel.  
           [0016]    A further object of the present invention is to provide a quick adjustment mechanism in accordance with the preceding object in which the trip handle can be easily manipulated to lock and unlock the trip handle in relation to a semicircular guide rigidly affixed to and extending above the shaft of the power trowel operating handle.  
           [0017]    A still further object of the present invention is to provide a quick adjustment mechanism for the blade pitch of a rotary power trowel in accordance with the preceding objects in which the control lever is pivoted at a central point on the operating handle of the trowel, a connecting rod is pivotally connected to the end of the control lever remote from the trip handle, the connecting rod is pivotally connected to a pivot link which is pivotally mounted on the operating handle, and a tension cable is connected to the pivot link on the side opposite the connecting rod. The tension cable extends downwardly along the operating handle to a point of connection with the swash plate actuating mechanism to vary the pitch of the blades with the mechanism of the control lever, connecting rod and pivot link providing a mechanical advantage leverage to enable the pitch of the blades to be adjusted with a minimum of force applied to the trip handle.  
           [0018]    Yet another object of the present invention is to provide a quick adjustment mechanism as set forth in the previous objects in which the trip handle is lockingly engaged with the semicircular guide by a pivotal locking plate with a slot receiving the semicircular guide and locking the control lever and trip handle against movement by a wedging action against the arcuate upper and lower edges of the guide.  
           [0019]    Yet a further object of the present invention is to provide a quick adjustment mechanism as set forth in the preceding objects in which the locking plate is released by a trigger mechanism incorporated into the trip handle to enable the locking plate to be unlocked with the locking plate enabling free movement of the control lever in a direction opposite to that in which the control lever becomes locked thereby enabling easy unlocking of the control lever and trip handle to enable the pitch of the blades to be reduced and enabling the pitch of the blades to be increased by moving the trip handle in an opposite direction without requiring the release of the locking plate by actuating the trigger mechanism thereby simplifying the adjustment of the blade pitch.  
           [0020]    An additional object of the present invention is to provide a trip handle which has a latch mechanism engaging a plurality of indentations or notches on the semicircular guide with the latch being released by a trigger mechanism which releases the latch from the indentations in the semicircular guide, thus enabling the trip handle to move in either direction to decrease the pitch of the blades or increase the pitch of the blades.  
           [0021]    A final object of the present invention to be set forth herein is to provide a quick adjustment mechanism for blade pitch of a concrete power trowel in accordance with the preceding objects and which will conform to conventional forms of manufacture, be of simple construction and easy to use so as to provide a device that will be economically feasible, long lasting and relatively trouble free in operation.  
           [0022]    These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    [0023]FIG. 1 is a side elevational view of a rotary power trowel having quick adjustment mechanism for the blade pitch in accordance with the present invention.  
         [0024]    [0024]FIG. 2 is a perspective view of the quick adjustment mechanism in accordance with the present invention.  
         [0025]    [0025]FIG. 3 is a schematic longitudinal sectional view of the quick adjustment mechanism shown in FIGS. 1 and 2 illustrating details of the control lever, trip handle, semicircular guide, locking plate and trigger mechanism.  
         [0026]    [0026]FIG. 4 is a schematic sectional view illustrating another embodiment of a quick adjustment mechanism in accordance with the present invention in which the trip handle includes a latch structure engaging notches in the semicircular guide. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]    Although only two preferred embodiments of the invention are explained in detail, it is to be understood that the embodiments are given by way of illustration only. It is not intended that the invention be limited in its scope to the details of construction and arrangement of components set forth in the following description or illustrated in the drawings. Also, in describing the preferred embodiments, specific terminology will be resorted to for the sake of clarity. It is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose.  
         [0028]    The quick adjustment mechanism of the present invention is generally indicated by reference numeral  10  and is associated with a conventional rotary power trowel generally designated by reference numeral  12 . The power trowel  12  includes a rotary blade assembly generally designated by reference numeral  14  driven by a small internal combustion engine generally designated by reference numeral  16  and is provided with the usual operating handle generally designed by reference numeral  18  having a tubular shaft  19  and a handle bar assembly  20  at its upper end. Positioned in the tubular shaft  19  is a tension cable  22  which is connected at its lower end to a pivotal actuator  24 . The actuator  24  engages a swash plate that controls the pitch of the blades in the blade assembly  14  by pivoting the blades about radial axes in a conventional manner.  
         [0029]    The handle bars  20  are preferably pivoted to the upper end of the operating handle  18  for pivotal movement about a transverse axis in order to adjust the position of the handle bars in relation to the trowel to enable optimum position of the handle bars with respect to an operator. The operating handle  18  is also provided with a throttle control readily accessible to the operator of the trowel. Also, a dynamic clutch control is provided to automatically stop rotation of the blade assembly by causing the drive belt between the engine drive shaft and the gear case drive shaft to become slack, thereby stopping the blades from rotating. All of the foregoing, except for the quick adjustment mechanism  10 , the details of which are described hereinafter, represent conventional structure employed in known power trowels. Hence, it is not considered necessary to describe the details of these conventional components further.  
         [0030]    The quick adjustment mechanism  10  of the present invention includes a pivot link  30  supported from an upper end portion of the tubular shaft  19  by a pivot pin or bolt  32  extending through depending brackets  34  as illustrated in FIG. 3. An upper end of the pivot link  30  is of arcuate configuration as indicated at  36  and provided with a peripheral groove  38 . The arcuate configuration  36  is preferably a section of a circle having a defined radius. The peripheral groove  38  receives the upper end of cable  22  with the terminal end of the cable  22  being anchored to the end of the groove  38  as indicated at  40 . Thus, pivotal movement of the pivot link  30  about pivot point  32  will impart linear movement to the cable  22  which is under constant tension with the lower end connected to the pivotal actuator  24  due to the weight of the power trowel resting on the trowel blades as known in the art. As the pivot link  30  pivots, the arcuate upper end thereof swings about pivot point  32  so that the point of tangency between the cable  22  and the arcuate groove  32  is always within the interior of the tubular shaft  19 .  
         [0031]    The lower end  41  of the pivot link  30  extends laterally of the tubular shaft  19  and has an elongated actuating rod generally designated by reference numeral  42  connected at its lower extremity by a pivot pin or bolt  44 . The actuating rod  42  includes a connecting rod  43  and a pivotal adaptor  46  which receives one end of the connecting rod  42  and enables effective adjustable connection for the actuating rod  42  by the connecting rod  43  being threaded into the adaptor  46  or otherwise adjustably secured thereto.  
         [0032]    In order to pivot the pivot link  30  and move the cable  22 , a control lever generally designated by reference numeral  48  is pivotally mounted on the tubular shaft  19  upward of the pivot link  30  and toward handle bars  20 . The lower portion of the control lever  48  is in the form of a downwardly opening yoke  50  of inverted U-shaped configuration which straddles the tubular shaft  19  and is pivotally connected to the shaft  19  at pivot point  52 . The lower end of legs  54  of the yoke  50  are pivotally connected to the end of actuating rod  42  by a transversely extending pivot member  56  journalled between the ends of the legs  54  by a pivot pin or bolt  58 . The end of the connecting rod  43  extends diametrically through the pivot member  56  and is adjustably connected thereto by either screw threaded engagement, set screw, clamp or the like. Thus, when the control lever  48  is pivoted about pivot point  52 , the actuating rod  42  will impart pivotal movement to the link  30  for pivoting the link  30  about pivot point  32  and linear movement of the cable  22 . The cable  22  is under constant tension since it, in effect supports the entire weight of the trowel, inasmuch as the trowel is completely supported by the blade assembly thus urging all of the blades in the blade assembly toward a flat engagement or zero pitch engagement with the concrete surface being finished. When the control lever  48  is pivoted forwardly toward the trowel, the lower end of the control lever  48  moves the actuating rod  42  away from the trowel and also moves the lower end of the pivot link  30  away from the trowel causing the pivot link  30  to pivot about pivot point  32  in a counterclockwise direction as seen in FIGS. 1 and 3. This counterclockwise rotation causes the cable  22  to move toward the trowel thus relaxing the cable tension. Relaxing the cable tension reduces the pressure on the actuator  24  and swash plate to decrease the pitch of the blades in the blade assembly due to the weight of the power trowel.  
         [0033]    The control lever  48  is continuously biased toward a position in which the blades are at zero pitch due to the blades supporting the weight of the trowel. Movement of the control lever  48  toward a position to increase the pitch of the trowel blades can be accomplished by pulling the upper end of the control lever  48  toward the handle bar assembly. Thus, it is necessary to provide a locking arrangement to secure the control lever  48  in various angular positions to prevent gravity and the weight of the trowel moving the control lever to a position in which the pitch of the blades is flat or zero. A locking mechanism generally designated by reference numeral  60  is provided for the control lever  48  and includes a rigid semicircular guide  62  rigidly attached to the tubular shaft  19  at the ends thereof as by brackets  63 , welding or the like. The semicircular guide  62  includes an inner edge surface  64  and an outer edge surface  66  having a center coinciding with the pivot axis  52  for the control lever  48 . The transverse cross-sectional configuration of the guide  62  is rectangular and the surfaces  64  and  66  are preferably smooth, although they may be roughened as desired.  
         [0034]    The upper end of the control lever  48  is provided with a housing  68  having a hollow interior cavity  70  and arcuate slots  72  through which the guide  62  extends. The center of curvature of the slots  72  is coincident to the pivot axis  52  for the control lever  48  thereby enabling the control lever  48  to pivot about the pivot axis  52  as the slots  72  permit the housing  68  to move along the semicircular configuration of the guide  62 . The upper end of the control lever  48  includes a T-handle  74  connected to the housing  68  by connecting member  76 . The connecting member  76  has a vertical cavity  78  therein which faces the handle bar assembly.  
         [0035]    In order to lock the control lever  48  against movement in a direction to reduce the pitch of the trowel blades, the cavity  70  is provided with a locking plate  80 . The locking plate  80  includes an opening in the form of a slot  82  that conforms with and receives the guide  62  in a manner similar to the slots  72  in the housing  68 . The lower edge of the locking plate  80  is received and rests in a recess  84  in the lower portion of the cavity  70  in a manner that permits the locking plate  80  to pivot between a position normal or perpendicular to the edge surfaces  64  and  66  of the guide  62  and a position in angular (non-perpendicular) relation to the edge surfaces  64  and  66 . The cavity  70  also includes a pair of springs  86  located above and below the slot  82  which normally bias the locking plate  80  toward the non-perpendicular position in relation to the edge surfaces  64  and  66  of the guide  62  so that the edges of the slot  82  will frictionally engage the edge surfaces  64  and  66  of the guide  62 . This frictional engagement prevents the control lever  48  from pivoting in a direction toward the trowel thereby preventing the weight of the trowel to move the blade pitch to a zero angle.  
         [0036]    However, when the control lever  48  is moved toward the handle bars, frictional engagement between the top and bottom edges of the slot  82  and the edge surfaces  64  and  66  of the guide  62  will actually compress the springs  86  to enable the locking plate  80  to move to a normal or perpendicular relation to the guide  62 . This movement enables the T-handle  74  to be moved toward the handle bars  20  for tensioning the cable  22  for increasing the trowel blades to a desired pitch against the weight of the trowel. The locking plate  80  automatically locks the control lever  48  in its adjusted position when the rearward manual force has been released from the T-handle  74 .  
         [0037]    In order to release the control  48  lever for movement of the T-handle  74  toward the trowel, a trigger assembly generally designated by reference numeral  90  is incorporated into the control lever  48  along the surface thereof which faces the handle bars  20 . The trigger assembly  90  includes a pivotal yoke  92  having depending legs  94  straddling the housing  68  and being pivotally connected thereto adjacent the lower ends of the legs  94  by pivot pins or pivot bolt  96 . Extending upwardly from the yoke  92  is an actuating pad or button  98  which can move toward and away from the cavity  78 . The inner surface of the pad  98  is hollow and receives a coil spring  100 . The spring  100  has one end engaging a small projection  102  on the inner wall of the cavity  78  and the other end received in cavity  104  in the pad or button  98 , as illustrated in FIG. 3. Forward pressure against pad  98  will cause the yoke  92  to pivot toward the connecting member  76  and be partially received within the cavity  78  by compressing the spring  100 . The pad  98  is preferably in a position to be engaged by the thumb of an operator&#39;s hand when the hand is grippingly engaged with the T-handle  74 .  
         [0038]    When the yoke  92  is pivoted about pivot pins or bolt  96 , a lock release member  106  extending between the legs  94  of the yoke  92  and received in slots  108  in the walls of the cavity  70  will engage the upper end portion of the locking plate  80  and pivot it to a position normal or perpendicular to the surfaces  64  and  66  of the guide  62  by compressing the springs  86 . Movement of the locking plate  80  to its perpendicular position will release the locking engagement between the locking member  80  and the upper and lower edges of guide  62 . By moving the locking plate to normal relation to the guide  62 , the wedging and gripping action of the locking plate with respect to the guide  62  which occurs when the locking plate is in an angular relation to the guide (other than normal or perpendicular) will be released. This enables the control lever  48  to pivot about pivot axis  52  in a counterclockwise direction as seen in FIGS. 1 and 3.  
         [0039]    When moved in a counterclockwise direction, the upper end of the control lever defined by the T-handle  74  moves toward the trowel and the lower end of the legs  54  move in the opposite direction toward the handle bars. Movement of the legs rearwardly also moves the lower end  41  of the pivot link  30  toward the handle bars through actuating rod  42 , thereby enabling the tension cable  22  to move toward the trowel. The weight of the trowel can then pivot the trowel blades toward a lesser or zero pitch. When it is desired to change the pitch of the blades in the event of a concrete surface requiring blades having an increased pitch, it is only necessary for the operator to reach forwardly and grasp the handle  74  and pull it toward the handle bar assembly. The control lever and thus the pitch of the blades may be quickly adjusted by the operator merely reaching forward and grasping and pulling the T-handle toward the handle bars or reaching forwardly, grasping the T-handle and exerting pressure on and moving the trigger pad  98  forwardly in relation to the control lever  48  thereby releasing the control lever  48  by orientating the locking plate  80  in normal or perpendicular relation to the guide  62  thereby quickly decreasing the pitch of the blades to any degree desired by releasing pressure on the pad  98  after a desired pitch of the blades has been reached.  
         [0040]    A mechanical leverage advantage is incorporated into the quick adjustment mechanism of the present invention by virtue of the differences in the distance between the connections of the components and the pivot point of the control lever  48  and the pivot link  30 . The lever arm distance between the pivot axis  52  of the control lever  48  to the T-handle  74  is much greater than the lever arm distance between the pivot axis  52  and the pivot member  56  at the lower end of the control lever legs  54 . The mechanical leverage advantage is further enhanced by the longer lever arm distance between the pivot connection  44  at the lower end of the pivot link  30  and the pivotal support pivot  32  compared with the lever arm distance (radius) between the pivot  32  for the pivot link  30  and the point of engagement between the arcuate groove  36  and the tension cable  22 . This enables the operator to increase the pitch of the blades by exerting less force on the T-handle in order to move the T-handle and thus the upper end of the control lever toward the handle bar assembly. Also, by positioning the control lever  48  centrally of the operating handle  18  by utilizing the yoke structure  50  with legs  54  which straddle the shaft  19 , the T-handle  74  is equally accessible to either hand of the operator of the trowel.  
         [0041]    Likewise, the trigger mechanism is centrally located in relation to the operating handle  18  and T-handle  74 . The trigger mechanism can thus be equally operated by either hand of the operator. This ergonomically advantageous arrangement of the quick adjustment mechanism provides the operator with better control of the trowel by utilizing either hand to quickly adjust the pitch of the blades while maintaining control of the trowel with the other hand. It facilitates more efficient operation of the trowel with less energy expenditure thereby enabling the operator to more efficiently finish a concrete surface.  
         [0042]    [0042]FIG. 4 illustrates an alternative embodiment of the quick adjustment mechanism of the present invention. This alternative embodiment incorporates a different locking mechanism  160  including a modified control lever  148  and a modified semicircular guide  162 . All of the other components and their relationships to the tubular actuating handle, tension cable, connecting rod and pivot link remain the same. The lower end of the control lever  148  is connected to a connecting rod at pivot point  156  and is connected to a pivot link in the same manner as that illustrated in FIGS.  1 - 3 . In this embodiment of the invention, the semicircular guide  162  includes a plurality of teeth and notches  164  on the inner edge surface of the guide  162 ; the outer edge surface  166  of the guide is smooth.  
         [0043]    The modified control lever  148  includes a housing  168  having a downwardly extending yoke  150  straddling the tubular shaft  118 . The control lever  148  is pivotally connected to shaft  118  at pivot  152  which forms a pivot axis for the control lever  148  and also defines the center of the semicircular guide  162  which is rigidly affixed to the tubular shaft  118 . The upper end of the control lever  148  includes a handle  174  which may be in the form of a partially spherical knob, a longitudinally straight cylindrical member, a T-handle or the like, which is connected to the body  168  by a connecting member  176 . The connecting member  176  includes a longitudinal bore  178  which includes an enlarged upper cavity  179  opening upwardly at its upper end.  
         [0044]    The enlarged upper cavity  179  slidably receives a longitudinally extending operating button  190  connected to an operating rod  191  which slides in the longitudinal bore  178 . The portion of the connecting member  176  and the body  168  which connects with the yoke  150  is provided with a longitudinally extending middle cavity  192  slidably receiving a flange  193  on the rod  191  which is closely received within the cavity  192  for longitudinal sliding movement. A coil spring  194  is positioned around the rod  191  between the flange  193  and the lower end of the cavity  192  defined by the yoke  150 . The operating rod  191  extends through the upper end of the yoke  150  and into a lower cavity  195  in the yoke which extends beyond the semicircular guide  162 . The body  168  at the upper end of the yoke  150  includes arcuate slots  196  which receive the guide  162  to enable the control lever  148  to pivot about pivot axis  152 .  
         [0045]    The lower end of the rod  191  includes a locking member connected thereto generally designated by reference numeral  197 . The locking member  197  includes a latch pin  198  extending transversely of the inner edge surface of the guide  162  for selective engagement with the teeth or notches  164 . The latch pin  198  is connected to cross piece  199  extending between the yoke members  150  and connected to connecting members  200  which connect the longitudinal rod  191  with the transverse member  199 . When the button  190  is depressed against the face of coil spring  194 , the transverse member  199  is depressed and the latch pin  198  is disengaged from the teeth or notches  164  thus enabling the control lever to pivot about pivot axis  152 . When the latch pin  198  is released, the control lever can be pulled towards the handle bar assembly for increasing the pitch of the blades or permitted to move forwardly toward the trowel to permit the blade pitch to decrease. This structure permits the control lever to be locked in any position in increments determined by the spacial relation of the teeth and the notches formed therebetween.  
         [0046]    The control lever  148  incorporates the same mechanical advantage leverage as the control lever  48  in FIGS.  1 - 3  to enable quick adjustment of the blade pitch with less force being exerted against the handle  174  when exerting a pulling force to increase the pitch or controlling forward movement of the upper end of the control lever  148  when decreasing the pitch. The location of the release button  190  for the latch pin  198  is such that the thumb can effectively depress the button regardless of which hand of the operator is used to manipulate the control lever  148 . As in the embodiment illustrated in FIGS.  1 - 3 , the operating handle including tubular shaft  118  is provided with appropriate manual controls for the throttle setting of the engine driving the rotary trowel and a clutch for interrupting the power drive to the blades which is automatically actuated to stop the driving power to the rotary blades in the event the operator loses control of the trowel and the control handle spins in order to promptly transfer of power to the rotary trowel blades in a manner well known in the art.  
         [0047]    The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and, accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

Summary:
A rotary power trowel machine for finishing concrete surfaces and more particularly to a quick adjustment mechanism for the pitch of the blades. The quick adjustment mechanism includes a control lever mounted on the operating handle of the trowel in a position to be easily grasped and operated by a trowel operator. The control lever changes the blade pitch through a mechanical advantage linkage which reduces the force applied to the control lever to adjust the blade pitch. The control lever includes a locking mechanism to lock the control handle and linkage in selected positions to lock the blades at a desired pitch angle. The locking mechanism includes a semicircular guide mounted on the trowel operating handle and extending through openings in the control lever. A locking device on the control lever lockingly engages the guide and is selectively locked and released from an upper end of the control lever.