HYDRAULIC SYSTEMS FOR GRADING MACHINES

A hydraulic system for operating a circle drive gear of a grading machine includes a pump configured to output pressurized fluid, a directional control valve fluidly coupled to the pump, a bidirectional hydraulic motor located downstream of the directional control valve and fluidly coupled to the directional control valve via hydraulic lines. The hydraulic motor has an output shaft that is configured to be rotationally driven by pressurized fluid output by the pump. Dual counterbalance valves may be disposed within the hydraulic circuit of the directional control valve and hydraulic motor such that any gearbox driven by the hydraulic motor is protected from external opposing forces. Accordingly, motion in the circle drive system is hydraulically locked at the beginning and release of a circle rotation command with the help of fluid pressure in the hydraulic lines.

TECHNICAL FIELD

The present disclosure relates generally to grading machines, and more particularly, to hydraulic systems for motor graders.

BACKGROUND

Grading machines, such as motor graders, are typically used to cut, spread, or level materials that form a ground surface. To perform such earth sculpting tasks, grading machines include a work implement, also referred to as a blade or moldboard. The work implement may move relatively small quantities of earth from side to side, in comparison to a bulldozer or other machine that moves larger quantities of earth. Grading machines are frequently used to form a variety of final earth arrangements, which often require the work implement to be positioned in different positions and/or orientations depending on the sculpting task and/or the material being sculpted. The different work implement positions may include a blade cutting angle.

Grading machines often utilize hydraulic systems to provide functionality and control to various aspects of the machines. For example, some grading machines may utilize hydraulic brake systems, work implement systems, and/or steering systems.

A circle drive may control a position of a circle coupled to the work implement, and thus may adjust the blade cutting angle, for example. Different work implement positions may require different amounts of torque in order to adjust the work implement, especially when the work implement is engaged with material. At the beginning and/or release of a command to control the circle drive, the work implement and/or grading machine may encounter large ground forces which could back drive the motion of the circle. Further, rotating the circle and work implement while the work implement is under an excessive load can lead to slippage in the circle drive, excessive heat generation, and wear of any clutch and/or other gear train components. In some cases, during operation of the grading machine, the work implement (e.g., blade, moldboard) may impact with a heavy and/or immovable object, for example, a rock that is at least partially embedded within and protruding from the earth. The work implement may consequently transmit the forces encountered during such impacts into a driving arrangement of the machine, for example, an output shaft of a hydraulic motor that is configured to rotationally drive a circle drive gear of the grading machine.

Given the speed of the machine and its momentum when travelling on the ground surface, these forces could cause failure of one or more components associated with the driving arrangement of the machine. Hence, it would be advantageous to provide a system that mitigates a susceptibility of components in the driving arrangement from being exposed to such forces when the work implement and/or grading machine encounters resistance (e.g., imposed by the ground, heavy and/or immovable objects) in its path of travel.

DETAILED DESCRIPTION

FIG.1shows a grading machine100with a circle drive system200. In some embodiments, the grading machine100may be a motor grader. The grading machine100may include a front frame104and a rear frame106supported by wheels. An operator may steer the front frame104relative to the rear frame106about a pivot point from an operator cab116disposed on the front frame104, for example. The operator cab116may be configured to house a steering wheel, levers, joysticks, push buttons, and/or other types of user interfaces for controlling various systems of the grading machine100.

In some embodiments, a controller118may be in communication with one or more features of grading machine100. The controller118may receive inputs from and send outputs to, for example, user interfaces in the operator cab116and/or an interface remote from the grading machine100. For example, the grading machine100may include electrohydraulic and/or hydro mechanical hydraulic systems, and the controller118may control electrical switches and/or valves to operate hydraulic cylinders, motors, actuators, and/or electrical elements. The controller118may include one or more controllers each associated with one or more components or systems of the grading machine100. For example, the controller118may be in communication with a pump and/or directional control valves, as described in further detail herein.

The grading machine100may include a prime mover120(e.g., engine, motor) supported on the rear frame106, for example. The prime mover120may supply driving power for driven components of the grading machine100. Further, the prime mover120may be coupled to a pump or generator for providing hydraulic, pneumatic, or electrical power to the grading machine100.

The grading machine100may include a work implement110. In some embodiments, the work implement110may be a blade and/or a moldboard for helping grade soil. The work implement110may be used to cut, spread, level, and/or otherwise sculpt earth or other material traversed by the grading machine100. The work implement110may be mounted on a linkage assembly that allows the work implement110to be moved to a variety of different positions and orientations relative to the front frame104.

The grading machine100may include a drawbar130mounted to the front frame104via a ball and socket arrangement, for example. As shown inFIGS.1-2, the drawbar130may be coupled to a large, flat yoke plate132. The position of the drawbar130may be controlled by hydraulic cylinders, including, for example, a right lift cylinder134, a left lift cylinder136, a centershift cylinder138, and a linkbar140. A height (e.g., blade height) of the work implement110with respect to the surface being traversed below the grading machine100may be primarily controlled and/or adjusted with the right lift cylinder134and/or the left lift cylinder136. The right lift cylinder134and the left lift cylinder136may be controlled independently and, thus, may be used to tilt the work implement110. Based on the positions of the right lift cylinder134and the left lift cylinder136, the work implement110may be tilted relative to the traversed material, thus the right lift cylinder134and the left lift cylinder136may control tilt of the work implement110. The right lift cylinder134and the left lift cylinder136may also be used (e.g., simultaneously extended/retracted) to control the height of the work implement110relative to the grading machine100to control depth of the cut into the ground surface or a height of the work implement110above the ground surface. For example, for an aggressive cut or sculpting procedure, the right lift cylinder134and the left lift cylinder136may be extended such that the work implement110is extended away from the grading machine100to a lower depth. In some embodiments, if the grading machine100is performing a light sculpting procedure, is traversing a ground surface between sculpting procedures, and/or it is otherwise desirable for the work implement110to not contact the ground surface, the right lift cylinder134and the left lift cylinder136may be retracted such that the drawbar130and the work implement110are lifted up toward the grading machine100.

The centershift cylinder138and the linkbar140may be used to shift a lateral position of the drawbar130, and any components mounted to the drawbar130, relative to the front frame104(e.g., drawbar centershift). The centershift cylinder138may include one end coupled to the drawbar130and another end pivotably coupled to the linkbar140. In some embodiments, the linkbar140may include a plurality of position holes142for selectively positioning the linkbar140to the left or right to allow for further shifting of the drawbar130to a left or right side of the grading machine100by the centershift cylinder138.

FIG.2shows the circle drive system200of the grading machine100ofFIG.1. In some embodiments, the circle drive system200may include a gearing arrangement (not shown) to engage with and rotate a circle gear or circle210that adjusts the orientation of the work implement110. The circle210may be positioned under the yoke plate132or otherwise directly and/or indirectly coupled to the drawbar130. The circle210may include a plurality of teeth (not shown) that extend along an entire inner face of the circle210. In some embodiments, the circle210may be coupled to the work implement110via a support arm112.

The circle210may be rotated by the circle drive system200. In some embodiments, the circle drive system200may include a motor250and a gear box260. The motor250may be a hydraulic motor (e.g., bidirectional) coupled to one or more hydraulic lines252. In some embodiments, the motor250may be in communication with the controller118. The motor250may be any motor that includes or is coupled to a rotational output shaft (e.g., gerotor type hydraulic motor, gear motor, vane motor, axial plunger motor, radial piston motor). In some embodiments, although not shown, the circle drive system200may include more than one motor and associated gear box (e.g., front circle drive system and rear circle drive system).

The rotational output shaft of the motor250may drive the gear box260and, in turn, rotate the circle210. Although not shown, the gear box260may include an output shaft that engages with teeth on the inner portion of the circle210to rotate the circle210. The gear box260may be directly coupled to the motor250or may be coupled to the motor250via a gear coupling (not shown). In some embodiments, the gear box260may be laterally adjacent to the motor250. Moreover, the gear box260may include any gear arrangement (e.g., one or more epicyclic or planetary gear assemblies, spur gears, worm gears) to drive the rotation of the circle210. In some embodiments, the gear box260may include one or more epicyclic or planetary gear assemblies (not shown), and a gear coupling may couple the motor250to the gear box260and the internal planetary gear assembly.

In some embodiments, the gear box260may also include one or more slip clutches and/or brakes, which may help to protect the motor250and gear arrangement in situations where the work implement110and/or the circle210encounters a heavy or severe external load while traversing the ground surface. In some embodiments, the gear box260may include a combining interface, which can help connect gear couplings to the other portions of the gear box260. For example, combining interface may include an exterior with threaded holes or other coupling mechanisms to couple exterior components of the gear coupling to other portions of the gear box260. The gear box260may include a housing to enclose the gearing, and a support plate mounted on the yoke plate132to couple the circle drive system200to the linkage assembly.

The rotation of the circle210by the circle drive system200may adjust a circle angle and pivot the work implement110relative to the drawbar130. In some embodiments, a cutting angle may be defined as the angle of the work implement110relative to the front frame104, and the cutting angle may be controlled by a combination of the position of the circle210and the position of the drawbar130. Based on the effect of the circle drive system200, the circle210and the work implement110may be rotated clockwise or counterclockwise relative to the front frame104. In some embodiments, the circle210and the work implement110may be rotated up to about 75° clockwise and/or counterclockwise. In other embodiments, the circle210and the work implement110may be rotated 360° clockwise and/or counterclockwise. A 0° cutting angle may be created when the work implement110is arranged at a right angle to the front frame104.

In some embodiments, a circle angle sensor212(e.g., rotary sensor, inertial measurement unit) may be positioned on the circle210to measure an angular rotation of the circle210, and thus an angle of the work implement110. For example, the circle angle sensor212may be mounted in a centered position on the circle210. As another example, the circle angle sensor212may be mounted in an off-centered position on the circle210, and the circle angle sensor212and/or other internal components of the grading machine100may be used to calculate the position of the circle210and the work implement110based on a compensation or correction to account for the off-centered position of the circle angle sensor212. The circle angle sensor212may also help to prevent the work implement110from being positioned at such an angle where the work implement110may contact or otherwise interfere with the wheels. For example, the circle angle sensor212may be in communication with the controller118, and may warn the operator and/or limit rotation of the circle210if a selected position would position the work implement110at an angle where the work implement110may contact wheels and/or other portions of the grading machine100.

The grading machine100may include a plurality of hydraulic lines252to control hydraulic cylinders and/or hydraulic motors. The grading machine100may include a hydraulic pump (e.g., pump330). The hydraulic pump may supply high pressure hydraulic fluid through one or more hydraulic lines252to one or more hydraulic cylinders and/or hydraulic motors (e.g., motor250, bidirectional hydraulic motor350). In some embodiments, a low pilot pressure may be provided by a hydraulic pressure reducing valve, which can receive the high pressure hydraulic fluid and supply low pilot pressure to each hydraulic cylinder and/or hydraulic motor. Additionally, each hydraulic cylinder and/or motor may include an electrical solenoid and one or more hydraulic valves. The solenoid may receive one or more signals from the controller118to control and position/rotation each hydraulic cylinder/motor by configuring the flow of hydraulic fluid through the valves.

The delivery of the hydraulic fluid may be controlled by the controller118. In some embodiments, the controller118may control the delivery of hydraulic fluid through the hydraulic lines252to the motor250to control the position and/or orientation of the circle210and the work implement110.

In some embodiments, an operator may send a command (e.g., using a joystick) to a control valve (e.g., directional control valve310, directional control valve410, directional control valve412) via the controller118to rotate the circle210counterclockwise, for example. In response to the command from the controller118, the control valve may direct the flow of hydraulic fluid from the hydraulic pump to the motor250via the hydraulic lines252. In response to the pressurized flow of hydraulic fluid from the control valve through the hydraulic lines252, the output shaft of the motor250may be forced to rotate, thereby driving the output of the gear box260to engage with the inner teeth of the circle210and rotating the circle210counterclockwise according to the operator's command.

FIGS.3-6show various hydraulic circuits for a grading machine circle drive system.

As seen inFIG.3, in some embodiments, a hydraulic system300for controlling the work implement110of the grading machine100may include a pump330. The pump330may be configured to output pressurized fluid (e.g., hydraulic oil) therefrom, thus providing a flow of pressurized fluid within the hydraulic system300. The pump330may be any component which functionally interacts with the pressurized fluid to convert mechanical energy to hydraulic energy, and/or vice versa. As such, the term “pump” as used in connection with the pump330is meant to include and be defined as any one or more of a hydraulic pump, a hydraulic motor, as well as a combination hydraulic pump/motor. The pump330may be any fluid delivery pump, such as a piston pump, a gear pump, a gerotor pump, a screw pump, a centrifugal pump, etc., based on the application requirements. As a non-limiting example, the pump330could be a gear pump or gerotor including two meshing gears with one of the gears being an internal gear and the other gear being an external gear mounted within and eccentrically relative to the internal gear. As shown inFIG.3, the pump330may be a fixed displacement pump. However, in other embodiments, the pump330may be a variable displacement pump.

Additionally, in some embodiments, the pump330may be electronically and/or controllably connected to the controller118, such that the operation and actuation of the pump330can be controlled in response to one or more signals generated by the controller118and electronically transmitted to, and received by, the pump330.

Further, as shown inFIG.3, the hydraulic system300may include a directional control valve310fluidly coupled to the pump330via a supply line. The directional control valve310may be any type of control valve, such as, for example, mechanically operated, hydraulically operated, electro-hydraulic, pneumatic, or the like. In some embodiments, the directional control valve310may be a hydraulically operated valve. In other embodiments, the directional control valve310may be an electromechanically operated valve or any other type or configuration suitable for performing functions consistent with the present disclosure.

The directional control valve310may be in communication with the controller118for receiving control signals (e.g., circle rotation commands). In some embodiments, the directional control valve310may include a proportional valve element that may be spring biased and solenoid actuated (e.g., via a control signal from the controller118) to move the valve element among a plurality of positions between a substantially flow blocking position (or substantially closed position) and a fully opened position. The amount of pressurized fluid directed from the pump330may be a function of the position of the directional control valve310and, thus, the corresponding amount of flow area thereof. As such, the directional control valve310may be configured to regulate fluid pressure in the hydraulic lines252associated with the pump330. In some embodiments, the directional control valve310may further include first and second pilot lines upstream and downstream of the directional control valve310, respectively, for communicating reference load pressures to the directional control valve310.

As shown inFIG.3, the hydraulic system300may also include a bidirectional hydraulic motor350(e.g., with a fixed-displacement volume). The bidirectional hydraulic motor350may be located downstream of the directional control valve310. Moreover, the bidirectional hydraulic motor350may be fluidly coupled to the directional control valve310via a first delivery line and a second delivery line (e.g., hydraulic lines252). As illustrated inFIG.3, the bidirectional hydraulic motor350may have an output shaft configured to be rotationally driven by pressurized fluid output by the pump330via the first and second delivery lines.

The directional control valve310may be configured to start, stop, or change the flow of the pressurized fluid and, thus, control the rotation of the bidirectional hydraulic motor350. For example, the directional control valve310may be a solenoid operated, variable position, four-way, three-position valve movable between a first working position, a second position, and a neutral position. In the first working position, a first port of the bidirectional hydraulic motor350may be in fluid communication with the pump330and a second port of the bidirectional hydraulic motor350may be in fluid communication with a tank. In the second working position, the first port may be in fluid communication with the tank, and the second port may be in fluid communication with the pump330. In the neutral position, the flow from the pump330to the bidirectional hydraulic motor350may be blocked. As another example, the directional control valve310may include an independent metering valve (IMV) system that includes plurality of independently-operated valves.

The output shaft of the bidirectional hydraulic motor350may include, be coupled to (e.g., via a gear coupling), and/or otherwise engage with a gear box (e.g., gear box260) or other gearing arrangement for rotating the circle210of the grading machine100. For example, the gear box260may include one or more components of a planetary gear assembly, and the hydraulic system300may include a bevel gear, gear coupling, or any other appropriate gear assembly to engage with and/or drive one or more components of the planetary gear assembly.

In some embodiments, the output shaft of the bidirectional hydraulic motor350may include or be affixed to a sun gear of the planetary gear assembly. The sun gear may engage with a plurality of planet gears, which in turn engage with a ring gear. Each of the planet gears may be coupled via a carrier. The ring gear may be coupled to or include a drive shaft that includes a circle engaging gear. Rotation of the ring gear, via planet gears, drives the rotation of the drive shaft and the circle engaging gear. The circle engaging gear may engage with teeth on the internal face of the circle210such that rotation of the circle engaging gear rotates the circle210, and thus controls an angle of the work implement110. Many other planetary gearing configurations in which the rotationally driven output shaft of the bidirectional hydraulic motor350provides the input for the planetary gear assembly are contemplated.

In other embodiments, the hydraulic system300may include a worm (e.g., worm screw) affixed to a free end of the output shaft of the bidirectional hydraulic motor350, and a pinion (e.g., worm gear) may be directly coupled to one or more interior portions of the gear box260and may be laterally disposed to the worm. For example, a shaft may extend from the pinion and be coupled to the sun gear. Alternatively, the pinion may be directly or indirectly coupled to a carrier of the sun gear. Accordingly, in either aspect, rotation of the pinion may rotate the sun gear of the planetary gear assembly. In some embodiments, a first gear may be located at a first end of the pinion and may be disposed in selective engagement with the worm with the help of a clutch. Moreover, a second end of the pinion may be configured to bear a second gear that may be adapted to operatively drive the circle210.

As shown inFIG.3, the hydraulic system300may further include dual counterbalance valves340located between the directional control valve310and the bidirectional hydraulic motor350. Accordingly, mechanical springs within the dual counterbalance valves340may set a threshold that the hydraulic fluid pressure must exceed before the hydraulic system300allows any other hydraulic fluid flow. Advantageously, the hydraulic fluid pressure threshold established by the dual counterbalance valves340may save the bidirectional hydraulic motor350from being back-driven due to torque applied on the work implement110or other opposing forces that may reverse the intended rotation of the circle210. In this manner, the dual counterbalance valves340may hydraulically lock flow across the bidirectional hydraulic motor350to be in the commanded rotational direction at the beginning or release of a circle rotate command from the operator when pressure in the hydraulic circuit is below the threshold. Moreover, when the directional control valve310is in a neutral position, the dual counterbalance valves340may hydraulically lock flow across the bidirectional hydraulic motor350in either direction. Further, the dual counterbalance valves340may allow for a more modulated or smoother control over the rotation of the circle210since the hydraulic fluid pressure threshold regulates the dynamic opening (and thus outflow or circuit pressure relief) of one counterbalance valve based on the continual pressure build-up across the cross-port line as fluid freely flows through the check valve line of the other (closed) counterbalance valve into one side of the bidirectional hydraulic motor350.

In some embodiments, the dual counterbalance valves340may be configured such that the hydraulic fluid pressure threshold or valve setting (e.g., spring stiffness or winding) may be varied depending on the size of the grading machine100and/or the application. For example, the valve setting range of the dual counterbalance valves340may be from about 25,000 kPa (3,625 psi) to about 35,000 kPa (5,077 psi). In some embodiments, the actual valve setting may be about 27,500 kPa (3,989 psi). In this way, varying the valve setting may vary the hydraulic fluid pressure threshold for the hydraulic system. In some embodiments, the hydraulic fluid pressure threshold may correspond to a threshold load or torque on the motor250, one or more slip clutches within the gear box260, and/or the connection between the motor250or the gear box260and the circle210. The threshold load may correspond to (e.g., be equal to or less than) a maximum torque that a component of the circle drive system200can withstand. The hydraulic fluid pressure threshold may be manually or automatically adjustable based on the type of grading machine100, the type and/or temperature of material being traversed and/or graded, or other factors. For example, a user interface may allow the operator to select a severe grading application to be implemented by controller118by inputting the material being graded, the severity of the grading application (e.g., hard rocky material or frozen ground, soft gravel or snow), and/or the threshold load on work implement110. In response to the operator's inputs, the user interface may display a recommended hydraulic fluid pressure threshold and/or range. Additionally or alternatively, the grading machine100may automatically set the hydraulic fluid pressure threshold based on the operator's inputs. Alternatively, the dual counterbalance valve assembly may not easily allow variation to the hydraulic fluid pressure threshold via the mechanical spring to prevent tampering after being set.

In some embodiments, the dual counterbalance valves340may be housed within a dual counterbalance valve assembly. Further, one or more components of the hydraulic system300may be combined into one housing or separated into multiple housings.

As shown inFIG.4, in some embodiments, a hydraulic system400for controlling the work implement110of the grading machine100may include two directional control valves410,412, a dual counterbalance valve assembly440, and two bidirectional hydraulic motors450,452. The hydraulic system400shown inFIG.4may operate similarly to the hydraulic system300ofFIG.3, with the addition of a bidirectional hydraulic motor452working in parallel with the bidirectional hydraulic motor450with an additional directional control valve412to direct hydraulic fluid through a first delivery line and a second delivery line (e.g., hydraulic lines252), alongside the directional control valve410. Although two bidirectional hydraulic motors450,452are shown in the illustrated embodiment ofFIG.4, it may be noted that such a tandem configuration of hydraulic motors is exemplary in nature and hence, non-limiting of this disclosure. In alternative embodiments, the circle drive system200may include fewer or more hydraulic motors than that disclosed herein depending on specific requirements of an application. For example, the circle drive system200may include one hydraulic motor in lieu of two hydraulic motors disclosed herein. To that end, the above disclosure is explained in conjunction with one of the hydraulic motors. However, it may be noted that similar explanation is applicable for either of the bidirectional hydraulic motors450,452shown inFIG.4.

As shown inFIG.5, in some embodiments, a hydraulic system500for controlling the work implement110of the grading machine100may include a directional control valve510, a dual counterbalance valve assembly540, and a bidirectional hydraulic motor550. The hydraulic system500shown inFIG.5may operate similarly to the hydraulic system300ofFIG.3.

As shown inFIG.6, in some embodiments, a hydraulic system600for controlling the work implement110of the grading machine100may include two directional control valves610,612, a dual counterbalance valve assembly640, and two bidirectional hydraulic motors650,652. The hydraulic system600shown inFIG.6may operate similarly to the hydraulic system400ofFIG.4.

As shown inFIGS.5-6, a brake (e.g., brake560,660,662) is disposed on the output shaft of the hydraulic motor (e.g., bidirectional hydraulic motor550, bidirectional hydraulic motors650,652) and engages with the output shaft with the help of a spring force for reducing a rotational speed of the output shaft in a brake engage state. The brake operatively disengages from the output shaft in a brake release state with the help of fluid pressure in at least one of a first delivery line and a second delivery line (e.g., hydraulic lines252). The hydraulic systems500,600may further include a pressure reducing valve assembly570,670located downstream of and fluidly coupled to first and second delivery lines of the directional control valves510,610,612. The pressure reducing valve assembly570,670may include one-way check valves upstream of the inlet of the pressure reducing valve. The pressure reducing valve assembly570,670may be located upstream of a tank580,680. The pressure reducing valve assembly570,670may be fluidly coupled to the one or more brakes560,660,662via one or more brake control lines. In some embodiments, a return line of the pressure reducing valve assembly570,670may include an orifice sized to maintain a pressure in the brake control line within a predetermined difference range with respect to the hydraulic fluid pressure in the return line downstream of the orifice.

INDUSTRIAL APPLICABILITY

The various aspects of the hydraulic systems of the present disclosure may be used in any grading/sculpting machine or other machine having one or more bidirectional hydraulic motors (e.g., motor250). to assist an operator in positioning and orienting the work implement110and the circle210. Additionally, the disclosed method of using a dual counterbalance valve assembly (e.g., dual counterbalance valves340) within the hydraulic circuit may help prevent damage to one or more of the work implement110, the circle210, the motor250, and the gear box260during the rotation and positioning of the work implement110and the circle210.

The grading machine100may receive a circle rotation command to control the rotation of the circle210during a grading operation. For example, an operator may input a circle rotation command via a joystick or via a user interface, and the command may be transmitted to the controller118. Alternatively, the circle rotation command may be automatically initiated or received by the controller118through an automated grading procedure, for example, when the grading machine100is moving forward and/or executing a programmed procedure.

It is noted that grading machine100may include any number of circle drive systems200. The circle drive system(s)200may be coupled to various portions of the circle210, and each circle drive system200and its components may be different sizes. Furthermore, the controller118may be coupled to the one or more circle drive system(s)200. Including more than one circle drive system200may reduce the overall size of each circle drive system and/or the overall height. For example, the grading machine100may include two circle drive systems and may deliver as much or greater torque to the circle210with each circle drive motor being smaller than the circle drive motor (e.g., motor250) of a grading machine100with a single circle drive motor. Additionally or alternatively, each gear box may be smaller or include fewer planetary gear assemblies and deliver an equal or larger torque on the circle210than a single circle drive system. In one aspect, each gear box may include a limit on the amount of torque that may be delivered through the gear box and/or the gear reduction of the gear box. In this aspect, including more than one circle drive system and the corresponding more than one gear box may allow for a greater torque to be delivered and/or a greater gear reduction to take place when controlling the positioning of the circle210and the work implement110. Moreover, the position of the one or more circle drive systems200may allow for additional or larger support elements to be coupled to one or more of the drawbar130, the circle210, and the work implement110relative to the front frame104.

Using one or more planetary gear assemblies within the circle drive system200may help to deliver a greater amount of torque to the teeth on the internal face of the circle210or other components of the work implement110and the circle210. Such an increase in torque may be beneficial when adjusting a position of the work implement110and the circle210when the work implement110is engaged with material on a ground surface or is otherwise under the effect of external forces.

When using one or more planetary gear assemblies within the circle drive system200(e.g., instead of a worm and pinion), inclusion of dual counterbalance valves in the hydraulic system (e.g., hydraulic system300) may aid in preventing the motor250from being driven in reverse due to external forces acting on the work implement110. The grading machine100may include multiple hydraulic circuits and one or more dual counterbalance valve assemblies in order to help prevent damage to the circle drive system(s)200and grading machine100. Wear or damage to the work implement110, the circle210, the motor250, and the gear box260, or another component of grading machine100may necessitate expensive or time-consuming repairs or otherwise affect the performance of the grading machine100.

Using dual counterbalance valves340in the hydraulic circuit of a circle drive system sets a mechanical pressure threshold to help prevent damage to various components of the grading machine100, for example, prevent slippage in the circle drive system200, excessive heat generation, wear of a clutch or other gear train components, etc. This mechanical threshold may thus be implemented without using sensors or requiring any additional monitoring or processing to be performed by the controller118. Advantageously, this dual counterbalance valve solution is not susceptible to software or other computing errors and may not incur any lag time in use. Further, the dual counterbalance valves340may lock motion of the circle210without having to actively physically actuate a component (e.g., brake) or disconnect any gearing connection between the circle drive motor (e.g., motor250) and the gear box260. In this way, the dual counterbalance valve assembly (e.g., dual counterbalance valves340) may exist as a passive component within the hydraulic circuit.