Riding trowel with counter rotating rotors

In a powered riding trowel of the type having at least two adjacent rotor assemblies wherein said rotor assemblies include rotors which are counter rotating relative to one another, and wherein the rotors circumscribe a circular path during operation, the rotor assemblies being affixed to a framework such that the paths circumscribed by the rotors are spaced apart so that tangential forces developed along the circumference of the respective paths do not interact to reinforce one another.

The present invention relates, in a broad sense, to motorized riding, or 
ride on, trowels having at least two rotor assemblies in which the rotors 
are counter rotating and, more particularly, to improvements in such 
riding trowels, particularly when pans are used to enhance the finish of 
the surface of the concrete to be worked. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The riding trowel, perhaps has its genesis in early developments in the 
1970's. Prior to that time, green concrete surfaces were leveled and 
finished by hand, or with a single powered rotor, which achieved 
locomotion by being manipulated by the operator, thus the colloquial 
designation, walk behind trowel. 
It is a universal truth, not only in the construction industry, but in the 
business world, that time is money. Thus, as the size of concrete pads has 
grown, so too has the time it takes to finish the surface. The ride on 
trowel was a pioneering effort to increase efficiency and cut down on 
labor costs in the cement finishing field. 
Since the advent of the first motorized ride on trowels, there have been 
several advances, many of which have been fathered by the present 
inventor. An advance in the art, however, often brought with it a new set 
of problems, and when the present inventor developed the ride on trowel 
having counter rotating rotors, a distraction was found to be inherent, 
which, although not a significant detriment, was an impediment to the 
optimal efficiency that this development would otherwise provide. 
The next step forward, again by the present inventor, was in the use of 
pans on riding trowels to further enhance the finish that these motorized 
devices could achieve. The pans are literally cylindrical bodies with a 
flat bottom portion. The pans fit snugly over the rotor blades and are 
driven by the rotating blades in a rotary motion. The flat bottom surface 
applies an exceptionally smooth finish to the surface of the green 
concrete being worked, as distinguished from the rotating blades of a 
rotor assembly, which tend to leave a spiral pattern of concentric circles 
defined by minute, or at least hopefully minute, ridges in the surface. 
Even with the use of pans and, in some instances, especially the use of 
pans, resulted in the undesirable formation of a ridge and some rippling 
of the green concrete along a path that essentially bisected the plane 
defined by the drive shafts of adjacent rotors. The time honored way of 
correcting such deformities in the surface of the concrete, is to go over 
the effected area again, perhaps with a walk behind, or by making a pass 
with a ride on in a different direction. That solution, however, requires 
additional time and fuel and is, therefor, not a truly satisfactory 
resolution of the problem. 
It is within this environment that the present invention was created. 
2. Overview of the Prior Art 
As previously mentioned, the Holz U.S. Pat Nos. 3,936,212 and 4,046,484 
appear to have been the progenitor of the ride on trowel. While the world 
knew that one could steer a walk behind trowel by tipping the rotor 
assembly one way or another, it was Holz that first synthesized that 
knowledge, and applied it to a power trowel having at least two rotor 
assemblies in order that the operator, sitting atop the device, could 
steer it from that location. 
It was, Allen, however, who advanced the quantum of knowledge in the field 
by improving the steerability of ride on trowels, as memorialized in his 
U.S. Pat. No. 5,108,220. The art was further advanced with the advent of 
the contra-rotating rotors, as described in the Allen U.S. Pat. 
application Ser. No. 08/587,014. Again, in Allen U.S. Pat. No. 5,480,257, 
the use of pans, and a means of accommodating pans on a rotor machine is 
presented for those skilled in the art. That disclosure includes means for 
adjusting the position of the rotor assemblies a small amount relative to 
the frame to accommodate the pans, the use of which obviates the use of 
any overlap between and among the blades of the adjacent rotors. 
While the forgoing constituted significant improvements, particularly in 
the steerability and performance of ride on trowels, with those 
improvements came new challenges in the form of certain problems, as 
articulated above, which Allen has set out to ameliorate, and has now done 
so, successfully. 
SUMMARY OF THE INVENTION 
With the foregoing by way of background, it will be seen that a primary 
objective of the present invention is to provide a motorized riding trowel 
having a minimum of two rotor assemblies in which the rotors rippling of 
the surface of the concrete to be worked is, if not entirely eliminated, 
substantially minimized. 
It is an adjunct to the foregoing objective to accomplish that objective 
without decreasing the efficiency of the subject machine, or materially 
adding to the labor and other costs incident to the finishing process. 
A further objective of the present invention is to enhance the efficiency 
of a multi-rotor riding trowel of the type wherein the rotors counter 
rotate, by eliminating problems inherent in the area of a bisection of the 
plane defined by the axes of rotation of adjacent rotors. 
Finally, but certainly not exhaustively, it is an objective of the present 
invention to accomplish all of the foregoing objectives with no diminution 
of the otherwise excellent steering and handling characteristics of the 
trowel over which the present invention represents an improvement. 
The foregoing, as well as other objects and advantages of the present 
invention, will become clear upon reading the following detailed 
description, taken in conjunction with the accompanying drawings, wherein:

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
With reference now to the accompanying drawings, and initially to FIG. 1, a 
riding trowel improved in accordance with the present invention is broadly 
designated by the reference numeral 20. The trowel 20, is generally of a 
now familiar configuration, and includes a frame 25 equipped with a pair 
of substantially identical twin rotor assemblies 27, which for purposes of 
this description, comprise generally a motor, motor driven gear box and an 
attached rotor 29, comprising, inter alia, a series of radially outwardly 
projecting blades 30. 
The rotors 29 are driven by the motor through the gear box, and they are 
counter rotating, such that as viewed from the operator's perspective, and 
shown in FIGS. 3 and 4, the left rotor is driven in a clockwise direction, 
and the rotor on the left rotates in a counterclockwise direction. When 
the rotors 29 and, thus, the blades 24 on each are rotated, they 
circumscribe a circular path P. 
The trowel 20 is constructed about a durable metal frame 25. Depending from 
the frame 25 is a guard cage 32, that surrounds the rotor assemblies 27 as 
a safety measure, in order to inhibit unintentional contact by foreign 
objects, animate and inanimate, with the rotor assemblies during 
operation. During use, the rotor assemblies support the trowel 20 on the 
concrete surface C to be finished by operation of the trowel. 
As referenced above, the trowel depicted is a two rotor trowel. It will be 
appreciated, however, that the improvements that are disclosed herein are 
equally applicable to any multiple rotor configuration so long as there 
are two adjacent rotors that are turning in opposite directions. 
Returning to FIGS. 1 and 2, the frame 25 mounts and secures for operation 
as part of the rotor assemblies 27, a pair of motors or engines 40, 45 
that drive the rotor assemblies 27, respectively, in opposite directions, 
as more particularly described above. 
Depending from each motor driven gear box, which is not clearly shown, but 
now well known in the art, are stub shafts 57 and 58, respectively. Each 
stub shaft is connected, in any suitable and well known fashion, to a 
central hub 60, forming the axis of each one of the rotors 29, thus 
completing the power circuit from motor to rotor. The blades 30 extend 
radially outwardly from the hub 60, as seen in FIGS. 3 and 4. 
The blades 30, as is now recognized in the art, frictionally interact with 
the concrete surface C to be finished and coincidently support the trowel 
20 and its operator during operation of the trowel. 
As stated from the beginning, the present invention relates to riding, or 
ride on, trowels, and, to that end, an operator station 65, which includes 
a seat 66 is mounted to the top of the frame 25, extending above the deck 
D which reposes on the frame 25, adding not only strength, but a safe 
place for the operator to perform his or her function. 
The trowel, in order to provide a steering function, as well as finish 
control, is fitted with a plurality of relatively sophisticated operating 
controls conveniently disposed within easy reach of a seated operator. The 
controls, and their function in the scheme of things, are the subject of 
one or more patents issued to the present inventor. 
In the depicted configuration, the operator steers the trowel 20 by means 
of two primary control levers 70, 75 (FIG. 1), respectively. The levers 
70, 75 are so constructed as to manipulate gearboxes, which comprise a 
part of the rotor assemblies 27, and which functionally interconnect each 
motor 40, 45 and an associated rotor 29 through stub shafts in the manner 
previously described. 
As is taught in Allen U.S. Pat. No. 5,108,220, the attitude of each gear 
box is independently determined at any given moment by the operator, and 
the attitude of the gearboxes determines the angle or degree of tilt of 
each of the rotor assemblies 27 to thereby generate steering forces. 
Movement of the trowel along a selected path is the result of reactive 
frictional forces generated on the surface of the concrete by the position 
and direction of rotation of the rotors 29, as the blades rotate, scraping 
against the concrete surface C. 
The operator also has at his disposal, means for determining the pitch of 
each group of blades 30 defining, with the hub 60, a rotor 29, and any 
suitable means, including manual, fluid driven, and electrical may be 
employed without departure from the invention, although manual controls 80 
are illustrated. Adjustment of the angle of the blades relative to the 
surface C permits the operator to control the quality of the finish being 
applied to that surface. 
As briefly referenced above, and as may be envisioned by particular 
reference to FIGS. 3 and 3A, a vertical plane is defined by the stub 
shafts 57, 58 and at a point P which bisects a line L--L stretched between 
the stub shafts within that plane, the forces generated by the counter 
rotating blades reinforce one another, and are thus multiplied, since 
along that line, and at the point of bisection, the blades of each of the 
rotors are moving, at the point P, in the same direction, and the 
tangential forces, graphically depicted by vectors V, generated at the 
tips of the blades as they arrive at point P are united, and consequently 
magnified by at least a factor of two, in the direction of travel, either 
a forward or aft direction, dependent on the direction of rotation of the 
rotors 29. There is, of course, an equal and opposite reactive force 
generated on the green concrete surface. 
The magnitude of the effect of these forces on the concrete surface to be 
finished depends on several factors, not the least of which is the gross 
weight of the trowel 20, and operator, and the state of the cure and mix 
of the concrete. 
By way of example, if the trowel is relatively lighter, and the concrete 
well along in the curing process, the reactive forces on the concrete will 
cause the trowel to be propelled in a direction opposite to the vectors V. 
As the trowel becomes relatively heavier, and where the concrete 
relatively green, the result is a gouging and rippling of the surface C, 
as seen in FIG. 3A at G, which is highly detrimental to the finishing 
process. 
The problem is exacerbated when the operator is attempting to guide the 
trowel in the forward direction, which as seen in the FIG. 3 
configuration, would be accomplished by tilting the rotors 29 toward one 
another. More precisely, in order to effect forward progress, the rotor 
assemblies are tilted downwardly in the area of point P, applying more 
forces in that area. Under such circumstances, it will be apparent to 
those skilled in the art, that gouging and rippling as at G is not only 
more likely, the severity interruption of the continuity of the concrete 
surface C that can be anticipated is significantly increased. 
Having thus isolated and defined the problem, a solution offered by the 
present invention, is graphically represented in FIGS. 4 and 4A, and now 
described. Specifically, the circular paths circumscribed by the rotor 
blades 30 must be positioned such that the tangential forces V generated 
at the tips 85 of each rotor blade are not concentrated and, thus, unable 
to reinforce one another to cause a multiplication, thereby constraining 
the total forces acting on the green concrete at a point P, particularly 
during forward steering movements, to no more than the actual tangential 
forces generated at the tip of each blade as it moves along the 
circumferential path. Thus, the forces experienced at the concrete 
surface, do not adversely disturb the surface being finished. 
Coincidently, it is imperative that the steering and handling 
characteristics of the trowel, which are considered excellent in the art, 
be undisturbed. 
In order to accomplish these objectives, the distance separating the stub 
shafts 60, and coincidently, the hubs of each rotor in the vertical plane 
defined by those shafts is, in keeping with the invention, increased. 
While it is known in the art that the distance between rotors may be 
manipulated slightly by adjusting the position of the rotor assemblies to 
eliminate overlap in the circular paths of the rotors to thereby permit 
the use of pans, such a nominal movement would be, and is, unsatisfactory 
as a means of vitiating the problems herein recognized. 
Thus, the present invention contemplates a spacing of adjacent rotor 
assemblies which will prevent reinforcing of the tangential forces 
generated at the tips of the blades. 
To this end, adjacent rotor assemblies are positioned on the frame 25 in 
order that the distance between the rotor hubs 60 is in a preferred range 
between twice the diameter of the path circumscribed by the rotor blades 
and 11/4 times such diameter. In order to effect the desired spacing, it 
may be necessary to stretch, or elongate, the frame to accommodate the 
increase in the distance between adjacent rotors, which increase may be up 
to an amount equal to the diameter of the rotors. 
By way of example, in a riding trowel in which the rotors are 46 inches in 
diameter, the distance between adjacent hubs 60 would range between 23 and 
46 inches, and the frame 25, where necessary, would reflect that spacing. 
While there may be some latitude in the ideal range of spacing, the result 
to be achieved, however, is the consistent elimination of ridging and 
rippling of the surface of the concrete being finished. 
While the separation of the rotors disclosed herein creates a path between 
the rotors that is unfinished by the trowel, it is common practice to make 
more than one pass over the surface during the finishing process. The 
unfinished swath, therefore, is readily finished in a subsequent path. It 
would be extremely difficult in several subsequent passes, however, to 
cure the damage that is caused by the tangential forces V multiplying to 
create the ridging and rippling described above.