STROKE CONTROL TROWEL

Inventors: Steven K. Hanson;

Brian L. Hammond;

David Lillianthal;

Benjamin A. Wiese;

Bruce R. Gillespie;

Robert Dane Davis; and

Cole R. Baird

PRIORITY/CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of U.S. Provisional Application No. 61/561,551, filed November 18, 2011, the disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

[0002] The present disclosure relates to speed control for hydraulically steered, riding power trowels.

BACKGROUND

[0003] The process of finishing concrete through the concrete curing phases with a self- propelled power trowel is ever changing. Riding power trowels are used for finishing concrete surfaces as the concrete is curing and hardening. A typical riding power trowel is a two-rotor device, with each rotor having a plurality of troweling blades extending out in radial fashion, and usually configured such that the working edge of each blade is in a plane perpendicular normal to the axis of rotation to provide for smooth and flat finishing of the concrete surface below the riding trowel. There is provided a rigid frame that houses the rotor assemblies, and also an engine, usually a gasoline or diesel engine, which provides the motive power for the rotor assemblies and thus the trowel blades. Atop of the engine and the frame assembly is found an operator's seat and the necessary control systems and levers for operation of the machine. These machines are manufactured in a variety of sizes and weights, with the largest of these machines having not just two, but rather three, rotor and troweling blade assemblies.

[0004] For purposes of this prior art section and the entire specification, a two-rotor machine will be used as an example. In two-rotor machines, both rotor assemblies rotate in opposite directions, one to the other. This is shown in Fig. 1.

[0005] In Fig. 1, there is shown a two-rotor assembly, wherein each rotor assembly has a gear box, hydraulic drive motor or other means of driving rotation, and troweling blade assemblies that rotate around respective axes of rotation, identified as A _RL for the axis of rotation for the left rotor, and A _RR as the axis of rotation for the right rotor assembly. Early versions of riding power trowels were mechanically steered. That is, the riding operator manipulated levers that were mechanically connected to the rotors to steer the trowel. But more recent riding trowels utilize hydraulic steering.

[0006] The hydraulically controlled steering power trowel is formed of the same basic subassemblies, including a rigid frame, engine assembly, operator seat and manual trowel blade pitch control systems, all of which are well known in the art. Also included are left control post and right control post that house, respectively, a left control valve assembly and a right control valve assembly. In a typical device, both the left and right control valve assemblies are proportional pressure output hydraulic valves capable of delivering and maintaining a selectable pressure to a dual-action hydraulic cylinder. U.S. Patent No. 5,876,740 ('740 Patent) discloses a hydraulically controlled steering power trowel, and the '740 Patent is incorporated herein by reference. It should be understood that designations "left" and "right," as used here, are arbitrary; and the functions of what are designated in this disclosure as the "left" and "right" may be accomplished, at the designer's preference, by applying the operable principles to any riding trowel regardless of which of the several assemblies is designated "left" or "right."

[0007] The left control valve assembly is operably interconnected between the frame of the power trowel and the left rotor assembly, and is used to adjust the tilt of the left rotor assembly either inwardly toward the center line of the frame, or outwardly away from the center line of the frame. The left control valve assembly is a single-action proportional pressure output valve that is operable to maintain a selectable hydraulic pressure within one or the other sides of the left dual- action hydraulic cylinder and is operably connected to the left rotor assembly to provide a tilting, either in or out from the center line movement for the left rotor assembly.

Hydraulic power is provided by a standard hydraulic pump that is operably connected to the trowel engine.

[0008] Again, only one rotor assembly, which in this example is the left rotor assembly, is only tiltable in and out from the center line. This is achieved by use of a universal drive assembly that is provided to interconnect the output drive shaft of the engine assembly to the rotor assembly. The universal drive assembly is capable of allowing the tilt motion for the left rotor either in or out relative to the center line of the power trowel.

[0009] Likewise, the right rotor assembly is interconnected by means of a dual-action universal assembly to the output drive assembly of the engine, and is therefore tiltable not only in an in- and-out direction relative to the center line, but it is also capable of being tilted either in a forward or aft direction. The right rotor assembly is provided with a right lever tilt post and a right forward and aft tilt post. Attached to the right lever tilt post is a dual action right tilt cylinder that is interconnected between the frame and the right tilt lever. In a similar manner, a second dual- action cylinder, the right forward and aft tilt cylinder, is interconnected to the right forward and aft tilt post and is anchored to the frame. The right control valve assembly is a dual action control system, and is operable to maintain a selectable hydraulic pressure in either side of both the right tilt cylinder and the right forward and aft cylinder, thus controlling not only the tilt of the right rotor assembly, but also its forward and aft movement. [0010] Both left and right control valve assemblies are fitted with joysticks that are configured such that if they are pushed forward, both rotor assemblies will tilt inwardly to move the power trowel forward, and conversely, if tilted backward toward the operator, they will operate to tilt the rotors outwardly to move the machine backward. The guidance system just described was fully disclosed in the Applicant's '740 Patent. What the prior art lacks, however, is a means for regulated adjustment of rotational speed of the rotor assemblies.

SUMMARY OF DISCLOSURE

[0011] The disclosed device is a speed control system for a power trowel that is configured to have regulated adjustment of rotational speed of the rotor assemblies. In this way, the power output of the trowel can be automatically regulated and can be adapted to utilize advanced control features such as cruise control and power management.

[0012] The power trowel for which the speed control system is designed includes, at a minimum, a power transfer unit, which is typically in the form of a hydraulic pump but could take other embodiments. The power trowel, on which the speed control system is incorporated, also includes, at a minimum, a pair of rotor assemblies that contact the concrete surface and support the frame and the power plant on the concrete surface. The rotor assembl ies are attached to the frame and configured to tilt in order to provide direction control for the power trowel . The rotor assembl ies incl ude a num ber of trowel blade assem blies with attached trowel blades, with trowel blades configured for adjusta ble pitch.

[0013] The power trowel incl udes, at a minimum, a first user input device for pitch control of the trowel blades. The second user input device controls the tilt control of the rotor assemblies. The third user input device is for control of the speed of rotation of the trowel blades and provides what is referred to throughout this disclosure as the user command or reference signal. This third user input device would typically be a pedal, but could also be a joystick or a shift knob or dial or a digital screen with digital control. The third user input generates a desired speed signal— i.e. a user command or reference input- indicative of the trowel user's desired rotational speed of the rotor assemblies.

[0014] In the hydraulic motor version of the device, the user command changes the pump displacement and thus changes the speed of rotation of the rotor assemblies. The disclosed device includes, at a minimum, a first sensor that measures blade speed. The measurement of blade speed can be a direct measurement of the angular speed of the rotating blades, or it can be measured indirectly by sensing the pump stroke or pump displacement or the hydraul ic motor's revol utions per minute ( PM). In the preferred embodiment and best mode presently known, pump stroke is measured to determine blade speed. The first sensor generates a speed feed back signal that is sent to a logic controller with the feed back signal indicative of the speed of rotation of the rotor assem blies. The disclosed speed control device incl udes, at a minimum, a logic controller for control ling the speed of rotation of the trowel blades by changing either the engine RPM or the displacement of the pump. The logic controller accomplishes this by sending a control signal to the power plant or the pump displacement controls. I n the preferred em bodiment, the logic controller changes the displacement of the hydraulic pump, which adjusts the rotational speed of the rotor assem blies.

[0015] The logic controller contains one or more logic patterns for correlating the reference input signal, engine load signal, and speed feedback signal with the control signal. The primary logic pattern that is in the logic controller is the "follower logic pattern." The follower logic pattern takes a reference input signal from the operator or other logic patterns and a speed feed back signal, from which two signals the logic controller generates a control signal that is continually adjusted so that the difference between the speed feedback and reference input signals are minimized.

[0016] To clarify, the signals in the follower logic pattern include:

(1) The reference input signal, which is from the operator and

may be scaled by various user controls, and is used to input

a desired rotor assembly rotational speed;

(2) The speed feedback signal, which is from the rotor assembly

or assemblies and is used as a feedback means to adjust the

control signal, and which can be a first speed feedback signal

and a second speed feedback signal if the rotor assemblies

are independently controlled; and

(3) The control signal from the logic controller, used to control

rotor assemblies' rotational speed, which can be a first

control signal and a second control signal if the rotor

assemblies are independently controlled.

[0017] Another logic pattern is the "cruise control" or "cruise function" logic pattern. This logic patter may be activated by a cruise control switch or activation button. When the cruise control logic pattern is activated, the reference input signal is locked at the value recorded at the moment the cruise control switch was activated. This locked reference input signal is then used by the logic controller and other logic patterns to generate a control signal.

[0018] Another logic pattern is a "power management" logic pattern. The power management logic pattern takes a load feedback signal and scales the reference input signal to generate a scaled reference input signal. Scaling the control signal adjusts the rotor assemblies' rotational speed, thereby reducing the power requirements from the power plant and preventing overloading. This scaled reference input signal is then used by the logic controller and other logic patterns to generate a control signal. The cruise control and power management logic patterns may be used in combination with the follower logic pattern, whereby the cruise control locks in, and power management scales the reference input signal.

[0019] Another logic pattern is the matching logic pattern. The matching logic pattern takes compares feedback signals from each rotor assembly and adjusts the respective control signal such that the control signal for each rotor assembly matches the other.

[0020] Although the hydraulic pump disclosed here would typically be a variable displacement pump, the speed control system and each of the logic patterns would also function with a fixed displacement pump and variable displacement motors.

BRIEF DESCRIPTION OF DRAWINGS

[0021] FIG. 1 is a prior art schematic representation of a mechanical control system of a two- rotor power trowel.

[0022] FIG. 2 is a perspective representational drawing of a hydraulically controlled riding power trowel with speed control.

[0023] FIG. 3 depicts an embodiment of the disclosure wherein the trowel is equipped with direct speed control.

[0024] FIG. 4 depicts an embodiment of the disclosure wherein the trowel is equipped with feedback speed control.

[0025] FIG. 5 depicts an embodiment of the disclosure wherein the trowel is equipped with master-slave, with feedback, speed control.

[0026] FIG. 6 depicts an embodiment of the disclosure wherein the trowel is equipped with dual logic, master-slave, with feedback, speed control.

[0027] FIG. 7 depicts an embodiment of the disclosure wherein the trowel is equipped with dual logic, single reference, with feedback, speed control.

EMBODI MENTS OF PRESENT DISCLOSURE

[0028] The disclosure may be implemented in a number of ways, depending on the preference of the designer and user. In one embodiment, depicted in FIG. 3, the trowel is equipped with direct control, via a reference input signal 104. The reference input signal is generated by a user input device (referred to above as a third input device), which allows the user to control the trowel speed in real time, much like an automobile driver controls speed with an accelerator pedal. This input device could be a foot pedal, a dial, a thumb wheel, a joystick, or other input device, and communicated to the rotor assemblies by way of hydraulic cylinders, servo valves/electric-over-hydraulic cylinders, or direct mechanical linkage.

[0029] In this or other embodiments, there could be provided a cruise control 108 (aka, cruise function) or a power management function, or both. When the cruise actuator 106 is engaged, the cruise control utilizes an electric or mechanical device for locking or maintaining the reference input signal 104. The cruise actuator comprises a means for engaging and

disengaging the cruise control. The cruise actuator could be a switch, level, toggle, push button, control screen setting, other user interface.

[0030] The power management function (aka power management logic) 112 utilizes load or engine feedback 110 from the trowel engine by monitoring the load of the rotor assemblies or the trowel engine, or both, utilizing a sensor or meter, or combination of sensors or meters. Further, the power management function relies on control logic to proportionally adjust the reference input to reduce machine loading as necessary to safely and efficiently operate the trowel. The reference input may thus be scaled by the power management function to create a scaled reference signal 116, which, in this embodiment, is equivalent to the control signal (118).

[0031] The trowel may also be equipped with control logic that incorporates other feedback signals in other respects. Embodiments such as that depicted in FIG. 4, rely on a speed feedback signal 220, which may include a signal relating the position of the rotor assemblies with respect to some pre-determined reference point, as measured by displacement or physical position of hydraulic cylinders; or it could include the rotor speed, as determined by a tachometer, or other angular speed-measuring device, on the rotor assembly; or it could include a signal relating the hydraulic fluid flow rate of fluid in and to the rotor assemblies, as measured by a flowmeter integrated into the rotor assemblies; or the feedback signal could comprise all or any of these. Furthermore, the trowel's engine is monitored via signals representing engine PM, percentage engine load, and the trowel's fuel delivery system. Such signals may come from any appropriate measuring device, including one or more tachometer, flowmeter, thermometer, and pressure meter.

[0032] In an embodiment that incorporates signal control with feedback— like the

embodiment shown in FIG. 4— there is provided a control logic 222 that processes a reference input signal 214, or scaled reference input 216, and speed feedback signal 220 as inputs and outputs a control signal 218 to the engine to ensure that the engine or rotor assemblies, or both, are not operated beyond tolerable limits, and that power to both rotor assemblies is equal.

[0033] In another embodiment, shown in FIG. 5, there is provided a control system that utilizes master-slave (aka, mother-daughter) control based on feedback, wherein the master control relies on a direct input from the user, while the slave control relies on feedback. In this embodiment, there is direct control via reference input signal 304, as described above, for control of pump displacement or engine speed of one rotor assembly, designated the "master" rotor assembly or assemblies. In other words, the master rotor assembly receives a control signal 318 equal to the reference input 314, or scaled reference input 316, signal. There is also provided a control logic 322 that accepts a speed feedback signal 320, of the type described above, from the master rotor assembly. In this embodiment, the speed feedback signal from the master rotor assembly is processed as a reference input signal in follower logic pattern of the control logic 322. The control logic 322 accepts a speed feedback signal (324) from the other, "slave," rotor assembly or assemblies, and outputs a control signal (326) to the slave rotor assembly. The control logic 322 utilizes a matching logic pattern to ensure that the slave rotor assembly is operating under power equal that of the master.

[0034] In another embodiment, shown in FIG. 6, there is provided a control system that utilizes master-slave control, wherein both master and slave rely on speed feedback. In this embodiment, there is provided a control unit with two logic steps 422 and 426. The first control logic step 422 accepts a reference input signal 404, which may be scaled by power management function 412 to create a scaled reference input 416, and a speed feedback signal 420 from one rotor assembly, designated the master. The first control logic step 422 outputs a control signal 418 to the master rotor assembly. The second control logic step 426 accepts a speed feedback signal 420 from the master rotor assembly, which functions as a reference input signal for the second control logic 426, and the second control logic also accepts a feedback signal 424 from the slave rotor assembly. The second control logic step 426 outputs a control signal 428 to the slave rotor assembly. The first control logic 422 ensures that reference 414 or scaled reference 416 input and feedback from the master rotor assembly are equal; and the second control logic 426 ensures that the feedback 420 from the master rotor assembly and feedback 424 from the slave rotor assembly are equal. In this way, the control system ensures that the master and slave are operating under equal power.

[0035] In another embodiment, shown in FIG. 7, there is provided a control system that controls both rotor assemblies individually, relying on speed feedback. In this embodiment, there is provided separate control logic for each of the master rotor assembly and the slave rotor assemblies. Both the master 522 and slave 526 control logic accept a reference input signal 504, which may be scaled by power management function 512 to become a scaled reference input 516. In both master 522 and slave 526 control logic, this is processed as a reference input. The master control logic 522 also accepts a speed feedback signal 520 from the master rotor assembly. The master control logic outputs a master control signal 518 to the master rotor assembly. The slave control logic 526 also accepts a speed feedback signal 524 from the slave rotor assembly. The slave control logic 526 outputs a slave control signal 528 to the slave rotor assembly. Both master and slave control logic ensure that the reference input signal or scaled reference input signal is equal to the respective feedback input signal to maintain equal operating power for each rotor assembly.

[0036] In addition to the example given above, it is contemplated that sensors/meters for creating signals can include dynomometers, PM sensors, tachometers, strain gauges, potentiometers, linear position sensors, and transducers. Any combination of these

sensors/meters could be implemented to monitor and provide the input or feedback signals, or both, which are described above.

[0037] One way this system would work is that it would act as a gear reduction strategy when a trowel is placed on wet concrete. At that time the motor tends to lug down, and stroke control would allow a gear down effect to help the motor out, and could even allow a smaller motor to be used for a particular job. This would provide a sort of continuously variable transmission based on hydraulic power, and could be analogous with mechanic devices which provide for mechanical adjustment of gear ratios.