BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to concrete finishing trowels which employ one or more rotatable blade-equipped rotor assemblies for finishing a concrete surface. More particularly, the invention relates to a concrete finishing trowel, such as a riding trowel, incorporating a torque transfer system for the rotor assembly or assemblies that has a variable speed ratio and that accommodates tilting of at least the driven shaft of the rotor assembly during a steering operation.

2. Description of the Related Art

A variety of machines are available for smoothing or otherwise finishing wet concrete. These machines range from simple hand trowels, to walk-behind finishing trowels, to self-propelled finishing trowels including some larger walk-behind machines as well as relatively large two-rotor or even three-rotor machines. Self-propelled finishing trowels, and particularly riding finishing trowels, can finish large sections of concrete more rapidly and efficiently than manually pushed finishing trowels. The invention is directed to self-propelled finishing trowels and is described primarily in conjunction with riding finishing trowels by way of explanation.

Riding concrete finishing trowels typically include a mobile frame including a deck. At least two, and sometimes three or more, rotor assemblies are mounted on an underside of the deck. Each rotor assembly includes a driven shaft extending downwardly from the deck and a plurality of trowel blades mounted on and extending radially outwardly from the bottom end of the driven shaft and supported on the surface to be finished. The driven shafts of the rotor assemblies are driven by one or more self-contained engines mounted on the frame and typically linked to the driven shafts by gearboxes of the respective rotor assemblies. The weight of the finishing trowel and the operator is transmitted frictionally to the concrete by the rotating blades, thereby smoothing the concrete surface. The individual blades usually can be tilted relative to their supports, via operation of a suitable mechanical lever and linkage system accessible by an operator seated on an operator's platform to alter the pitch of the blades, and thereby to alter the pressure applied to the surface to be finished by the weight of the machine. This blade pitch adjustment permits the finishing characteristics of the machine to be adjusted. For instance, in an ideal finishing operation, the operator first performs an initial “floating” operation in which the blades are operated at low speeds (on the order of about 30 rpm) but at high torque. Then, the concrete is allowed to cure for another 15 minutes to one-half hour, and the machine is operated at progressively increasing speeds and progressively increasing blade pitches up to the performance of a finishing or “burning” operation at the highest possible speed—preferably above about 150 rpm and up to about 200 rpm.

The blades of riding trowels can also be tilted, independently of pitch control for finishing purposes, for steering purposes. By tilting the driven shafts of the rotor assemblies, the operator can cause the forces imposed on the concrete surface by the rotating blades to propel the vehicle in a direction extending perpendicularly to the direction of driven shaft tilt. Specifically, tilting at least the driven shaft of the rotor assembly from side-to-side and fore-and-aft steers the vehicle in the forward/reverse and the left/right directions, respectively. It has been discovered that, in the case of a riding trowel having two rotor assemblies, the driven shafts of both rotor assemblies should be tilted for forward/reverse steering control, whereas only the driven shaft of one of the rotor assemblies needs to be tilted for left/right steering control.

The rotor assemblies of the typical riding finishing trowel are driven by a drive train that is connected directly to input shafts of the assemblies' gearboxes via a centrifugal clutch and a system of shafts, belts or chains, and other torque transfer elements of constant speed ratio. The drive trains also require universal joints to accommodate tilting of the gearbox relative to the remainder of the drive train during a steering control operation. The universal joints are expensive to maintain and must be maintained or replaced relatively frequently due to the ingress of concrete into the universal joints and their attendant bearings.

Another problem associated with traditional rotor assembly drive systems is that they exhibit an insufficient speed range for both low speed/high torque floating operations and high speed burning operations. The typical drive system includes a simple centrifugal clutch of a constant speed ratio. Hence, blade speed increases at least generally proportionately with engine speed from zero to a maximum speed, with torque decreasing commensurately over that same engine speed range. No known concrete finishing trowel has a constant speed ratio clutch that can obtain both the necessary low speed/high torque combination required for optimal floating operations and the high speed required for optimal burning operations. Hence, many contractors keep two machines at each job site—one having a relatively low speed ratio and configured for floating operations, and one having a relatively high speed ratio and configured for burning operations. This requirement significantly increases the expense of a particular finishing operation.

The above-identified problems associated with drive systems having traditional centrifugal clutches can be alleviated if the traditional centrifugal clutch is replaced with a hydrostatic drive system, as is the case in the HTS-Series Ride on Power Trowel marketed by Whiteman Corp. of Carson, Calif. However, hydrostatic drive systems still exhibit a less than optimal speed/torque range. They are also relatively expensive and heavy when compared to more traditional, mechanical-clutch operated drive systems. The hydraulic components of these hydrostatic systems are also prone to failure and leakage.

Applicants are aware of one attempt to alleviate these problems by using a variable speed ratio torque converter assembly to transfer torque from the engine to the rotor assemblies of a riding concrete finishing trowel. Specifically, Bartell Corp. proposed the use of a torque converter assembly to permit the speed ratio of a concrete finishing trowel's rotor assemblies to change during the operation of the machine. The torque converter assembly included drive and driven variable-speed clutches that operated in conjunction with one another so that, as the engine accelerated, the relative diameters of the sheaves of the drive and driven clutches changed to increase the machine's speed ratio as the engine speed increased. However, testing revealed that the clutches of this torque converter assembly were improperly sized and configured. As a result, the desired effect of providing a single machine capable of operating at low rpm and high torque and high rpm and low torque was not achieved.

OBJECTS AND SUMMARY OF THE INVENTION

It is therefore a first principal object of the invention to provide a concrete finishing trowel that includes a reliable, low-maintenance torque transfer system for coupling the driven rotor assembly or assemblies of the machine to the machine's engine or other power source.

Another object of the invention is to provide a concrete finishing trowel that meets the first principal object and that includes a torque transfer system which is relatively immune to damage from the ingress of wet concrete or other materials.

In accordance with a first aspect of the invention, these objects are achieved by eliminating the universal joint of a traditional rotor assembly drive system in favor of a flexible drive shaft that can bend to accommodate tilting of the rotor assembly driven shaft (or the gearbox if the flexible shaft is coupled to the driven shaft via an intervening gearbox) during a steering control operation. The flexible shaft, preferably comprising a flexible wound wire shaft, requires no universal joints and is maintenance free.

Another object of the invention is to provide a concrete finishing trowel that meets the first principal object and that can change speed ratios so as to permit the same machine to be used effectively for both low speed/high torque operations and high speed/low torque operations.

Another object of the invention is to provide a concrete finishing trowel that meets at least the first principal object and that does not require expensive, heavy, and leak-prone hydraulic systems to increase the machine's speed range.

In order to increase the effective operational range of the machine, a variable speed ratio torque converter assembly is preferably used to couple, at least indirectly, the driven shafts of the rotor assemblies to the engine. The torque converter assembly is configured such that it has a low speed ratio and high torque ratio at low engine speeds and exhibits progressively higher speed ratios as the engines input speed increases. Preferably, the torque converter assembly includes drive and driven clutches that are connected to one another by a belt or the like and that each has a sheave of variable effective diameter. At initial clutch engagement, the effective diameter of the drive clutch sheave is very small (due to the fact that the axial width of the drive sheave is maximized), and the diameter of the driven clutch sheave is very large (due to the fact that axial width of the driven sheave is minimized), resulting in a low speed/high torque ratio and yielding the lowest rotor speed and highest rotor torque. As the engine speed increases, the drive sheave begins to narrow axially, causing the drive sheave effective diameter to increase and tightening the drive belt. Drive belt tightening forces the driven sheave components apart so that the driven sheave widens axially, thereby causing the effective diameter of the driven sheave to decrease and increasing the speed ratio. Ultimately, the effective diameter of the drive sheave becomes very large, and the effective diameter of the driven sheave becomes very small, resulting in a very high speed ratio. As a result, a single machine can be used to perform both low speed/high torque floating operations and high speed burning operations.

Another principal object of the invention is to improve the versatility of a concrete finishing machine by permitting the diameter of the circular areas finished by the rotor assemblies of a multi-rotor assembly machine to be varied to meet the needs of a particular application.

In accordance with another aspect of the invention, this object is achieved by mounting the blades of each of the machine's rotor assemblies on the associated driven shaft such that the diameter of each of the circular areas is adjusted by changing a radial spacing between ends of the blades and the associated driven shaft. Preferably, each rotor assembly comprises a plurality of support arms which extend radially outwardly from the driven shaft and on which the trowel blades are mounted, and the trowel blades are mountable on multiple axial locations on the support blades so as to alter the diameter of the circular area. If the finishing trowel has a pair of rotor assemblies, the first and second rotor assemblies are dimensionally adjustable to adjust the diameter of the circular areas finished by the rotor assemblies to permit the finishing trowel to be operated in either an overlapping mode or a non-overlapping mode.

Another principal object of the invention is to provide an improved method of transferring torque from an engine or other power source of a concrete finishing trowel to one or more rotor assemblies of the machine using equipment that is simple, inexpensive, and reliable.

In accordance with another aspect of the invention, these objects are achieved by transferring torque from a power source, such as the output shaft of an internal combustion engine, to a shaft which is flexible along at least a substantial portion of the entire length thereof, then transferring torque from the flexible shaft to a driven shaft of a rotor assembly of the finishing trowel, and then, during the torque transfer operation, repeatedly tilting the driven shaft with respect to the frame of the finishing trowel, thereby causing the flexible shaft to dynamically and repeatedly bend during torque transfer.

The flexible shaft preferably comprises a wire wound flexible shaft and typically will be connected directly to the input shaft of the gearbox of the rotor assembly. Preferably, the flexible shaft is coupled to the gearbox input shaft or another shaft to which it is attached so as to permit relative axial movement therebetween occurring upon tilting of the rotor assembly during a steering control operation.

Another object of the invention is to provide a method that meets the second principal object and that permits the machine to be used through a wide range of speeds and torques so as to permit the same machine to be used for both high torque/low speed operations and high speed operations.

The machine can be operated so as to perform a low speed/high torque floating operation and a high speed burning operation using the same machine. As a result, torque is transmitted to each rotor assembly of the machine so as to rotate at speeds of less than 50 rpm, and preferably on the order of 30 rpm, during a floating operation and at over 150 rpm, and preferably on the order of 200 rpm, during a burning operation. In addition, the blades can be moved along their arms so as to operate in either an overlapping mode or a non-overlapping mode.

These and other objects, advantages, and features of the invention will become apparent to those skilled in the art from the detailed description and the accompanying drawings. It should be understood, however, that the detailed description and accompanying drawings, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred exemplary embodiments of the invention are illustrated in the accompanying drawings in which like reference numerals represent like parts throughout, and in which:

FIG. 1

is a perspective view of a riding concrete finishing trowel constructed in accordance with a preferred embodiment of the invention;

FIG. 2

corresponds to FIG.

1

and illustrates the finishing trowel with the operator's seat and adjacent shrouds removed;

FIG. 3

is a right side sectional elevation view of the finishing trowel, taken through the right rotor assembly of the machine;

FIG. 4

is a left side sectional elevation view of the finishing trowel, taken through the left rotor assembly of the machine;

FIG. 5

is a partially fragmentary, partially schematic sectional end elevation view of the finishing trowel;

FIG. 6

is a partially exploded, perspective view of the right rotor assembly of the finishing trowel, along with the associated steering linkage and actuators;

FIG. 7

is a front elevation view of the assembly of

FIG. 6

;

FIG. 8

is a side elevation view of the assembly of

FIGS. 6 and 7

;

FIG. 9

is a top plan view of the assembly of

FIGS. 6-8

;

FIG. 10

a partially exploded perspective view of the left rotor assembly of the machine, along with the associated steering linkage and actuator;

FIG. 11

is a top plan view of the assembly of

FIG. 10

;

FIG. 12

is a sectional side elevation view of the assembly of

FIGS. 10 and 11

;

FIG. 13

is a schematic illustration of the electronic control components of a steering control system constructed in accordance with a first preferred embodiment of the invention;

FIG. 14

is a schematic illustration of the electronic control components of a steering control system constructed in accordance with a second preferred embodiment of the invention;

FIG. 15

is a sectional side elevation view of the finishing trowel, illustrating a torque transfer system of the machine;

FIG. 16

is a partially fragmentary, partially schematic top plan view of the torque transfer system of

FIGS. 14 and 15

;

FIG. 17

is an exploded perspective view of the torque transfer system of

FIGS. 14-16

;

FIG. 18

is a bottom plan view of the finishing trowel with its blades configured for non-overlapping operation;

FIG. 18A

is a fragmentary sectional elevation view of a portion of a rotor assembly of the finishing trowel configured as illustrated in

FIG. 18

;

FIG. 19

is a bottom plan view of the finishing trowel with its blades configured for overlapping operation; and

FIG. 19A

is a fragmentary sectional elevation view of a portion of a rotor assembly of the finishing trowel configured as illustrated in FIG.

19

.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

1. Resume

Pursuant to the invention, a concrete finishing trowel is provided having one or more driven rotor assemblies coupled to an engine or other power source of the machine by a novel torque transfer system including at least one flexible shaft and possibly including a variable speed ratio torque converter assembly. The flexible shaft, preferably comprising a flexible wound wire shaft, bends to accommodate tilting movement of the associated rotor assembly that occurs upon a steering operation, thereby eliminating the need for high-maintenance universal joints or other, less durable equipment. The torque converter assembly, preferably taking the form of a pair of variable speed clutches each having variable diameter sheaves, permits the speed and torque ratios of the drive system to change with increases in engine speed so that the same machine can be effectively used for both low speed/high torque floating operations and for high speed burning operations. Multi-application use is further facilitated by moving the blades axially along their support arms to permit the blades to operate in either an overlapping mode or a non-overlapping mode.

2. System Overview

The present invention is applicable to any power concrete finishing trowel that is steered by tilting of the rotor assembly or rotor assemblies of the trowel. Hence, while the invention is described herein primarily in conjunction with a riding finishing trowel having two counter-rotating rotor assemblies, it is not so limited.

Referring now to

FIGS. 1-6

and initially to

FIG. 1

in particular, a riding concrete finishing trowel

20

in accordance with a preferred embodiment of the invention includes as its major components a rigid metallic frame

22

, an upper deck

24

mounted on the frame, an operator's platform or pedestal

26

provided on the deck, and right and left rotor assemblies

28

and

30

, respectively, extending downwardly from the deck

24

and supporting the finishing machine

20

on the surface to be finished. The rotor assemblies

28

and

30

rotate towards the operator, or counterclockwise and clockwise, respectively, to perform a finishing operation. A conventional ring guard

32

is positioned at the outer perimeter of the machine

20

and extends downwardly from the deck

24

to the vicinity of the surface to be finished. The pedestal

26

is positioned longitudinally centrally on the deck

24

at a rear portion thereof and supports an operator's seat

34

. The pedestal

26

and seat

34

can be pivoted via hinges (not shown) to permit access to components of the machine located thereunder, such as the machine's engine

72

. A fuel tank

36

is disposed adjacent the left side of the pedestal

26

, and a water retardant tank

38

see

FIG. 1

is disposed on the right side of the pedestal

26

and overlies one of the actuators

86

of a steering system

76

detailed below.

A lift cage assembly

40

, best seen in

FIGS. 2 and 5

, is attached to the upper surface of the deck

24

beneath the pedestal

26

and seat

34

. The lift cage assembly

40

is formed from a plurality of interconnected steel tubes including front and rear generally horizontal tubes

42

and

44

spaced above the deck

24

by vertical support tubes

46

positioned at the ends of the generally horizontal tubes

42

and

44

. The front and rear generally horizontal tubes

42

and

44

are connected to one another by a plate

48

that has D-shaped cutouts

50

(

FIG. 5

) to provide a central lifting location for receiving a hook or the like. The cutouts

50

are positioned such that the entire machine

20

can be lifted from a central lift point, thereby eliminating the need for a harness or a four-point type attachment usually used to lift machines of this type for transport.

Referring now to

FIGS. 3-5

, each rotor assembly

28

,

30

includes a gearbox

52

, a driven shaft

54

extending downwardly from the gearbox, and a plurality of circumferentially-spaced blades

56

supported on the driven shaft

54

via radial support arms

58

and extending radially outwardly from the bottom end of the driven shaft

54

so as to rest on the concrete surface. Each gearbox

52

is mounted on the undersurface of the deck

24

so as to be tiltable about the deck

24

for reasons detailed below.

The pitch of the blades

56

of each of the right and left rotor assemblies

28

and

30

can be individually adjusted by a dedicated blade pitch adjustment assembly, generally designated

60

in

FIGS. 1-4

. Each blade pitch adjustment assembly

60

includes a generally vertical post

62

and a crank

64

which is mounted on top of the post

62

, and which can be rotated by the operator to vary the pitch of the trowel blades

56

. In the typical arrangement, a thrust collar

66

cooperates with a yoke

68

that is movable to force the thrust collar

66

into a position pivoting the trowel blades

56

about an axis extending perpendicular to the axis of the driven shaft

54

. A tension cable

70

extends from the crank

64

, through the post

62

, and to the yoke

68

to interconnect the yoke

68

with the crank

64

. Rotation of the crank

64

adjusts the yoke's angle to move the thrust collar

66

up or down thereby providing a desired degree of trowel blade pitch adjustment. A power concrete finishing trowel having this type of blade pitch adjustment assembly is disclosed, e.g., in U.S. Pat. No. 2,887,934 to Whiteman, the disclosure of which is hereby incorporated by reference.

Both rotor assemblies

28

and

30

, as well as other powered components of the finishing trowel

20

, are driven by a power source such as a gasoline powered internal combustion engine

72

mounted under the operator's seat

34

. The size of the engine

72

will vary with the size of the machine

20

and the number of rotor assemblies powered by the engine. The illustrated two-rotor, 48″ machine typically will employ an engine of about 25 hp. The rotor assemblies

28

and

30

are connected to the engine

72

via a unique torque transfer system

74

(

FIGS. 15-17

) and can be tilted for steering purposes via a unique steering system

76

(FIGS.

6

-

14

). The steering system

76

and torque transfer system

74

will now be described in turn.

3. Steering System

As is typical of riding concrete finishing trowels of this type, the machine

20

is steered by tilting a portion or all of each of the rotor assemblies

28

and

30

so that the rotation of the blades

56

generates horizontal forces that propel the machine

20

. The steering direction is perpendicular to the direction of rotor assembly tilt. Hence, side-to-side and fore-and-aft rotor assembly tilting cause the machine

20

to move forward/reverse and left/right, respectively. The most expeditious way to effect the tilting required for steering control is by tilting the entire rotor assemblies

28

and

30

, including the gearboxes

52

. The discussion that follows therefore will describe a preferred embodiment in which the entire gearboxes

52

tilt, it being understood that the invention is equally applicable to systems in which other components of the rotor assemblies

28

and

30

are also tilted for steering control.

More specifically, the machine

20

is steered to move forward by tilting the gearboxes

52

laterally to increase the pressure on the inner blades of each rotor assembly

28

,

30

and is steered to move backwards by tilting the gearboxes

52

laterally to increase the pressure on the outer blades of each rotor assembly

28

,

30

. Side-to-side steering requires tilting of only one gearbox (the gearbox

52

of the right rotor assembly

28

in the illustrated embodiment), with forward tilting of the gearbox

52

increasing the pressure on the front blades of the rotor assembly

28

to steer the machine

20

to the right. Similarly, rearward tilting of the gearbox

52

increases the pressure on the back blades of the rotor assembly

28

to steer the machine

20

to the left.

The steering system

76

tilts the gearboxes

52

of the right and left rotor assemblies

28

and

30

using right and left steering assemblies

80

and

82

controlled by a controller

85

. The right steering assembly

80

, best seen in

FIGS. 5-9

includes a first or right actuator arrangement and a first or right steering linkage

88

coupling the right actuator arrangement to the gearbox

52

of the right rotor assembly

28

. Similarly, the left steering assembly

82

, best seen in

FIGS. 10-12

, includes a second or left actuator arrangement and a second or left steering linkage

92

coupling the second actuator arrangement to the gearbox

52

of the left rotor assembly

30

. The first actuator arrangement includes both a forward/reverse actuator

84

and a left/right actuator

86

, whereas the second actuator arrangement includes only a forward/reverse actuator

90

. The controller

85

preferably is coupled the actuators

84

,

86

, and

90

so that manipulation of the controller

85

in a particular direction steers the machine

20

to move in that same direction, preferably at a speed that is proportional to the magnitude of controller movement.

The actuators

84

,

86

, and

90

extend vertically through the deck

24

of the concrete finishing trowel

20

and are attached directly or indirectly to the frame

22

, e.g., by attachment to the deck

24

and/or to the lift cage assembly

40

as best seen in

FIGS. 2-5

. Each actuator may comprise any electrically-operated device that selectively receives energizing current from the controller

85

in the form of electrical steering command signals and translates those command signals into linear movement of the output of the actuator and resultant pivoting of the associating steering linkage

88

or

92

. The actuators

84

,

86

and

90

preferably are of the type that have internal feedback potentiometers which compare the actual position of the actuator's output with the commanded position transmitted by the controller

85

. When those positions match, actuator motion stops, and the actuator holds its output in that position. Suitable actuators comprise ball-screw actuators available, e.g., from Warner Electric of South Beloit, Ill. These actuators are bi-directional, versatile, relatively low-cost, and feedback controlled. Each actuator

84

,

86

, or

90

includes 1) a stationary base

94

extending above the deck

24

and fixed to the deck or another stationary component of the machine

20

, 2) an electric motor

96

, and 3) a linearly-displaceable rod

98

. The rod

98

is driven by a ball screw drive, which provides precise positioning and high load carrying capacity. For instance, an actuator of this type can provide saddle speeds up to 49″ per second and drive axial loads up to 900 lbs. The preferred actuator has a force rating of approximately 500 lbs., though lighter-duty actuators could be used if the steering linkages

88

and

92

were to be replaced by more complex lever assemblies. It should be emphasized, however, that ball-screw actuators of this type are not essential to the invention and that other electrically-powered actuators could be used in their stead.

Each of the left and right steering linkages

88

and

92

will now be described in turn.

Referring to FIGS.

3

and

5

-

9

, the right steering linkage

88

includes a steering bracket

100

and a pivoting support assembly mounting the steering bracket

100

on the deck

24

for biaxial pivoting movement with respect thereto. The pivoting support assembly includes first and second pairs of pillow block bearings

102

and

110

, and a cross tube

104

. The first pair of pillow block bearings

102

is bolted to the bottom of the deck

24

. The cross tube

104

has 1) opposed longitudinal ends

106

journaled in the pillow block bearings

102

and 2) opposed lateral ends

108

disposed adjacent the second pair of pillow block bearings

110

. The steering bracket

100

includes a frame

112

extending longitudinally of the machine

20

and a pair of mounting plates

114

extending laterally from the frame

112

. The steering bracket

100

and gearbox

52

are fixed to the second pair of pillow block bearings

110

by bolts

116

extending through holes in the pillow block bearings

110

, through mating holes in the mounting plates

114

, and into tapped bores in the top of the gearbox

52

. By this arrangement, the steering bracket

100

(and, hence, the gearbox

52

) 1) pivots about a lateral axis of the cross tube

104

to effect fore-and-aft tilting of the gearbox and, accordingly, left/right steering and 2) pivots about a longitudinal axis of the cross tube

104

to effect side-to-side gearbox tilting and, accordingly, forward/reverse steering control. To enable gearbox pivoting about the cross tube's longitudinal axis, a longitudinal end of the frame

112

of the steering bracket terminates in a clevis

118

which is coupled to the output of the left/right actuator

86

by a pivot pin

120

. In the illustrated embodiment, the opposite end of the frame

112

presents a mounting plate

122

for the blade pitch adjustment post

62

(see FIG.

3

), thereby assuring that the blade pitch adjustment assembly

60

moves with the gearbox

52

and that a steering control operation therefore does not affect blade pitch. To enable gearbox pivoting about the cross tube's lateral axis, the output of the forward/reverse actuator

84

is pivotably connected to a clevis

124

of a pivot lever

126

via a pivot pin

128

. The lever

126

extends through the second pair of pillow block bearings

110

, through the lateral ends of the cross tube

104

, and is held in place by a retaining ring

130

.

Turning now to

FIGS. 2

,

4

,

5

and

10

-

12

, the left steering assembly

82

differs from the right steering assembly

80

only in that it is configured to pivot only side-to-side for forward/reverse steering operation. As a result, the clevis at the longitudinal end of its steering linkage

92

can be eliminated, along with the left/right actuator

86

. In addition, the second set of bearings

110

can be replaced with simple supports

150

. The left steering linkage

92

is otherwise identical to the right steering linkage and includes a steering bracket

140

and pivoting support assembly. The pivoting support assembly includes 1) pillow block bearings

142

and 2) a cross tube

144

having longitudinal ends

146

and lateral ends

148

. The steering bracket

140

includes a frame

152

and a pair of mounting plates

154

extending laterally from the frame

152

and connected to the supports

150

and the gearbox

52

via bolts

156

. The post

62

of the associated blade pitch adjustment assembly

60

is mounted on a mounting plate

162

mounted on one end of the frame

152

. The output of the forward/reverse actuator

90

is coupled to a clevis

164

of pivot lever

166

by a pivot pin

168

. The pivot lever

166

extends through the supports

150

, through the lateral ends

148

of the cross tube

144

, and is fixed to the supports

150

by spring pins

172

so that the gearbox

52

and frame

22

can pivot laterally about the longitudinal axis of the cross tube

144

but are fixed from longitudinal pivoting about the lateral axis.

The controller can be any device translating physical operator movements into electronic steering command signals. Turning now to

FIG. 13

, one preferred controller

85

for generating steering command signals and transmitting the steering command signals to the actuators

84

,

86

, and

90

is a dual-axis, proportional control joystick that is electronically coupled to the actuators via a programmed CPU

180

. The above-mentioned feedback capability of the actuators

84

,

86

, and

90

permits them to interface with the CPU

180

to correlate actuator motion with joystick motion. As a result, the appropriate actuator

84

,

86

, or

90

moves in the direction commanded by the joystick

85

through a stroke that is proportional to the magnitude of joystick movement. The machine

20

therefore moves in the direction of joystick movement at a speed that is proportional to the magnitude of joystick movement. For instance, to steer the concrete finishing machine

20

to move forwardly, the joystick

85

is pivoted forwardly about its fore-and-aft axis, and the CPU

180

controls both forward/reverse actuators

84

and

90

to extend or retract their output rods through a stroke that is proportional to the degree of joystick movement, hence driving the gearboxes

52

to pivot laterally toward or away from each other by an amount that causes the machine

20

to move straight forward or rearward at a speed that is proportional to the magnitude of joystick movement. Similarly, joystick movement from side-to-side about its second axis generates a steering command signal that is processed by the CPU

180

, in conjunction with the feedback potentiometers on the left/right actuator

86

, to extend or retract the output rod of that actuator

86

so as to tilt the associated gearbox

52

forwardly or rearwardly by an amount that is proportional to the magnitude of joystick movement and that results in finishing machine movement to the right or left at a speed that is proportional to the magnitude of joystick movement. If the joystick

85

is released and, accordingly, returns to its centered or neutral position under internal biasing springs (not shown), each of the actuators

84

,

86

, and

90

also returns to its centered or neutral position.

Still referring to

FIG. 13

, the joystick

85

includes a stationary base

182

and a grip

184

that is mounted on the base

182

and that is pivotable as described above. A rocker switch

186

is mounted on the grip

184

and is operable when depressed to energize both forward/reverse actuators

84

and

90

simultaneously (but in opposite directions) so as to effect either clockwise or counterclockwise turning of the machine

20

, depending upon the direction of rocker switch displacement. Preferably, the rocker switch

186

is configured such that the machine

20

turns clockwise when the rocker switch

186

is pivoted to the right and counterclockwise when the rocker switch

186

is pivoted to the left.

As an alternative to the above-described arrangement, the single dual-axis joystick

85

of

FIG. 13

can be replaced with two joysticks

85

R and

85

L as illustrated in

FIG. 14

, one of which (

85

R) is a dual-axis joystick suitable for both forward/reverse and left/right steering control and the other of which (

85

L) is a single-axis joystick which is pivotable only fore-and-aft to effect only forward/reverse steering control. The rocker switch is eliminated from this embodiment. Some operators might prefer this arrangement because it, like the conventional mechanical lever arrangements with which they are acquainted, uses a dedicated controller for each rotor assembly.

The above-described power steering system

76

exhibits many advantages over traditional mechanically operated systems and even over hydrostatically operated systems. For instance, it is much easier to operate than mechanically-operated systems, with the only forces required of the operator being the relatively small forces (on the order of less than 1-2 lbs) needed to overcome the internal spring forces of the joystick(s). In addition, much simpler mechanical linkages are required to couple the actuators

84

,

86

, and

90

to the gearboxes

52

than are required to couple mechanically-operated control levers to the gearboxes of earlier systems. Moreover, unlike hydrostatically steered systems, the machine

20

is relatively lightweight and does not risk high-pressure fluid spills.

4. Torque Transfer System

Referring now to

FIGS. 15-18

, the torque transfer system

74

is designed to transfer drive torque from an output shaft

200

of the engine

72

to the input shafts

202

of the gearboxes

52

so as to drive the rotor assemblies

28

and

30

to rotate. Significant novel features of the torque transfer system

74

include 1) its ability to change speed ratios and/or blade assembly diameters so as to permit the machine

20

to perform markedly different finishing operations and 2) its elimination of the need for a complex universal joint while still accommodating tilting movement of the driven shafts

202

of the gearboxes

52

relative to the engine output shaft

200

. These two goals are achieved using 1) a variable speed ratio torque converter assembly

204

(FIG.

16

), and 2) flexible drive shafts

206

(FIG.

17

), respectively.

The torque converter assembly

204

includes variable speed drive and driven clutches

208

and

210

coupled to one another by a torque transfer element, preferably a belt

212

. A hub

214

of the drive clutch

208

is keyed to the engine output shaft

200

(which may be either the actual output shaft of the engine

72

or another output shaft coupled directly or indirectly to the engine's output shaft) as illustrated in FIG.

16

. Similarly, a hub

216

of the driven clutch

210

is keyed to a jackshaft

218

so that the jackshaft rotates with the driven clutch

210

. The jackshaft

218

is supported on the frame

22

by pillow block bearings

220

and has output ends

222

that are coupled to the respective left and right flexible shafts

206

.

The flexible shafts

206

are coupled to both the jackshaft

218

and to the input shafts

202

of the gearboxes

52

. Specifically, and as can be seen in

FIG. 17

, each of the flexible shafts

206

is fixed to an associated output end

222

of the jackshaft

218

via a coupling

226

pressed into the associated bearing

220

. An input end of each coupling

226

is keyed to an associated output end

222

of the jackshaft

218

, and an output end of each coupling

226

is bolted to a fitting

224

swagged onto the input end of the associated flexible shaft

206

. Another fitting

228

, swagged onto an output end of each of the flexible shafts

206

, is coupled to the associated gearbox input shaft

202

by an internally splined coupling

230

bolted to the fitting

228

. The splined fitting

230

permits relative axial movement between the flexible shaft

206

and the gearbox input shaft

202

during gearbox tilting. If desired, this relative movement could also be achieved by permitting axial movement between the flexible shaft

206

and the jackshaft

218

.

As discussed briefly above, flexible shafts are used as the shafts

206

in order to accommodate tilting of the left and right gearboxes

52

relative to the jackshaft

218

without requiring complex universal joints. Each shaft

206

is formed from materials that permit it to bend along at least a substantial portion of the entire length thereof, typically all but at the ends and, while retaining sufficient torsional stiffness to permit the shaft

206

to drive the input shaft of the associated gearbox

52

. The shafts

206

need not bend a great deal because the gearboxes

52

only tilt a few degrees (less than 10° and typically on the order of 4°) in operation. However, and unlike most applications in which flexible shafts of this type are used, the shafts

206

bend dynamically (i.e., while they are transmitting torque) and repeatedly during operation of the machine

20

. A wound wire flexible shaft, often used in weed eaters and other equipment exhibiting a convoluted fixed path between the drive motor and the driven shaft, has been found to work well for this purpose. The illustrated shaft is in the range of 1′ long and 1″ in diameter. If desired, a sleeve

232

, formed from rubber or some other moisture and dirt proof material, can be fitted around the wound wire of the shaft

206

to protect it. A suitable wound wire shaft is available, e.g., from Elliott Manufacturing Company of Binghamton, N.Y.

The torque converter assembly

204

is preferably of the variable speed ratio type available, e.g., from Comet Industries. As best seen in

FIGS. 16 and 17

, drive clutch

208

includes the aforementioned hub

214

and a variable width sheave

240

. The sheave

240

includes a first portion

242

fixed to the hub

214

and a second portion

244

slidably mounted on the hub

214

so as to be axially movable towards and away from the first portion

242

. The second portion

244

is biased away from the first portion

242

by a spring (not shown) and movable axially towards the first portion

242

under the action of a plurality of centrifugal cams

246

. The inner axial faces of the first and second portions

242

and

244

are angled toward one another from the outer to inner radial ends thereof so that the effective radial diameter of the sheave

240

(corresponding to the location on the sheave

240

that is substantially the same width as the belt) varies inversely with the axial spacing between the first and second portions

242

and

244

. Accordingly, as the speed of the engine output shaft

200

increases, the centrifugal cams

246

force the second portion

244

towards the first portion

242

to decrease the effective axial width of the sheave

240

. The effective radial diameter of the sheave

240

therefore increases as the belt rides upwardly along the sheave in the direction of arrow

248

in FIG.

16

.

The driven clutch

210

also has a variable diameter sheave

250

, but the diameter of the sheave

250

varies inversely with the diameter of the sheave

240

of the drive clutch

208

. Specifically, the sheave

250

of the driven clutch includes a first portion

252

fixed to the hub

216

and a second portion

254

mounted on the hub

216

so as to be axially movable towards and away from the first potion

252

. The second portion

254

is biased towards the first portion

252

by a spring

256

. As with the drive clutch, the inner axial faces of the first and second portions

252

and

254

are angled toward one another from the outer to inner radial ends thereof so that the effective radial diameter of the sheave

250

varies inversely with the axial spacing between the first and second portions

252

and

254

. Accordingly, as the belt

212

moves outwardly along the sheave

240

of the drive clutch

208

during engine acceleration, the increased tension compresses the spring

256

to widen the axial gap between the first and second sheave portions

252

and

254

to reduce the effective diameter of the driven sheave

250

. As a result, the belt

210

rides inwardly in the direction of arrow

258

in FIG.

16

. The effective speed ratio of the torque converter assembly

204

therefore progressively increases upon engine acceleration, and progressively decreases upon engine deceleration as the reverse affect occurs. This permits the rotor assemblies

28

and

30

to be driven through a speed/torque range that varies dramatically with engine speed.

The invention takes advantage of this capability by being capable of operating in both overlapping and non-overlapping modes using the same machine

20

. Specifically, as best seen in

FIGS. 18

,

18

A,

19

, and

19

A, the trowel blades

56

are mounted on their associated support arms

58

by bolts

260

that extend through bores

262

spaced axially along the support arms

58

and into tapped bores

264

in mounting brackets

266

for the blades

56

. The support arms

58

are long enough and have enough mounting bores

262

to permit the blades

56

to be fixed to different points along the arms

58

so as to permit the trowel blades

56

to be mounted either 1) inwardly along the support arms

58

so that the two circles C

1

and C

2

circumscribing the blades

56

of the rotor assemblies

28

and

30

do not overlap, as seen in

FIGS. 18

, and

18

A; or 2) outwardly along the support arms

58

so that the two circles C

1

and C

2

circumscribing the blades

56

of the rotor assemblies

28

and

30

overlap, as seen in

FIGS. 19 and 19A

. When the blades