Multi-worm circle drive gearbox

A work vehicle comprises a frame, a circle gear mounted to the frame to rotate relative thereto, a moldboard coupled to the circle gear to rotate therewith, and a circle drive gearbox comprising gearing, a first worm, and a second worm, the gearing meshing with the circle gear, the first and second worms meshing with the gearing.

FIELD OF THE DISCLOSURE

The present disclosure relates to a work vehicle, such as, for example, a motor grader, having a circle drive for rotating a circle gear to which a moldboard is coupled.

BACKGROUND OF THE DISCLOSURE

A motor grader has a main frame, a draft frame coupled to the main frame for movement relative to the main frame, a circle gear mounted to the draft frame to rotate relative thereto about a central axis of the circle gear, a moldboard coupled to the circle gear to rotate with the circle gear, and a circle drive configured to rotate the circle gear relative to the draft frame.

A type of circle drive has a single-worm circle drive gearbox with a single worm that meshes with a worm gear operatively coupled to a pinion gear meshing with the circle gear, the worm and the worm gear providing a worm gear set of the circle drive. A single hydraulic motor of the circle drive is operatively coupled to the worm to apply torque to and rotate the worm gear set so as to rotate the circle gear and the moldboard coupled thereto selectively in opposite first and second directions about the central axis of the circle gear.

The worm gear set has a reduced useful life due to durability issues. The worm and the worm gear are made of dissimilar materials so that they do not weld themselves together during operation. The worm gear is made of a softer material than the worm so as to be the sacrificial part (e.g., worm gear made of high-strength manganese bronze and worm made of hardened steel). The sliding action between the worm and the worm gear causes wear on the worm gear, wear being a function of worm rotational speed and applied torque. As such, the worm gear eventually wears to the point of fracture, leading to downtime for replacement of the worm gear.

SUMMARY OF THE DISCLOSURE

According to the present disclosure, a work vehicle, such as, for example, a motor grader, comprises a frame, a circle gear mounted to the frame to rotate relative thereto, a moldboard coupled to the circle gear to rotate therewith, and a circle drive gearbox comprising gearing, a first worm, and a second worm. The gearing meshes with the circle gear. The first and second worms mesh with the gearing.

In an exemplary embodiment, the gearing comprises a worm gear, and the first and second worms mesh with the worm gear. The two worms and the worm gear provide a worm gear set.

The gearbox is included in a circle drive configured to rotate the circle gear relative to the draft frame. The circle drive further includes a hydraulic system configured to rotate the first and second worms. The hydraulic system comprises a hydraulic first motor and a hydraulic second motor. The first and second motors are flow-parallel to one another. The first motor is operatively coupled to the first worm. The second motor is operatively coupled to the second worm. Due to the flow-parallel arrangement, the circle drive is able to self-balance such that the worms apply the same torque to the worm gear and rotate at the same speed. Such operational equalization avoids seizure of the worm gear which may occur if the worms were not to balance in applied torque and rotational speed.

By way of comparison, assume, for example, that the first and second worms collectively apply the same overall torque (T) as the single worm of a single-worm circle drive gearbox. In such a case, each of the first and second worms individually applies approximately ½ (T) to the worm gear, rather than the full torque (T) as in the case of a single-worm. Due to such a torque reduction at each worm, compared to the single-worm circle drive gearbox, it is thought that the dual-worm circle drive gearbox would result in a reduced wear rate on the worm gear, increasing the useful life of the worm gear.

In another example, compared to a single worm that applies a torque (T) to the worm gear, use of two worms could increase the overall torque applied to the worm gear (e.g., 1.5T) while still decreasing the individual torque applied by each worm to the worm gear (e.g., approximately 0.75T). It is thought that this arrangement would result in a reduced wear rate, increasing the useful life of the worm gear.

The circle drive gearbox may have more than two worms (e.g., three), further dividing the torque applied by each worm to the worm gear. It is thought that this arrangement would result in a reduced wear rate on the worm gear, increasing the useful life of the worm gear.

The circle drive may actuate the worms in a number of other ways. For example, pneumatic or electric motors may be used in place of hydraulic motors. In another example, there may be a single motor (e.g., hydraulic, pneumatic, or electric) coupled mechanically to each worm via a differential. In yet another example, in lieu of a motor, the worms may be driven mechanically via a drive line from the engine or the transmission, with a differential between the drive line and the worms.

The above and other features will become apparent from the following description and the attached drawings.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring toFIGS. 1 and 2, there is shown respectively a work vehicle10and a sub-assembly thereof. By way of example, the vehicle10is illustrated and described below as a motor grader.

As a motor grader, the vehicle10has front and rear sections12,14. The front and rear sections12,14are articulated to one another at an articulation joint for steering of the vehicle10left and right using a left articulation cylinder and a right articulation cylinder, the articulation cylinders coupled to and extending between the front and rear sections12,14. The rear section14includes the internal combustion engine (e.g., diesel engine) of the vehicle.

The vehicle10exemplarily has six ground-engaging wheels. The front section12has two wheels, a left front wheel and a right front wheel. The rear section14has four wheels, two left rear wheels arranged in a tandem and two right rear wheels arranged in a tandem.

The front section12has an operator's station16from which a human operator can control the vehicle10. The operator's station is supported on the main frame18of the front section12.

The front section12has a moldboard20mounted to the main frame18of the front section12. The moldboard20is configured for moving earthen or other material.

The moldboard20is mounted for movement in a number of directions. A draft frame22is coupled to the main frame18toward the front via a ball-and-socket joint. A circle frame24is mounted to the draft frame22to rotate relative thereto about a central axis of a circle gear25of the circle frame24by use of a circle drive26having a multi-worm circle drive gearbox27engaging the circle gear25. A tilt frame28holds the moldboard20and is coupled pivotally to the circle frame24for pivotal movement of the tilt frame28and the moldboard20held thereby relative to the circle frame24about a tilt axis by use of a tilt cylinder29. The moldboard20is coupled to the circle frame24and thus its circle gear through the tilt frame28to rotate with the circle frame24and its circle gear relative to the draft frame22.

A saddle30is mounted to the main frame18. Left and right blade-lift cylinders32(only the left blade-lift cylinder is shown) are connected to the saddle30and the draft frame22therebetween for raising and lowering the sides of the draft frame22, and thus the moldboard20, relative to the main frame18.

A circle side-shift cylinder34is connected to the saddle30and the draft frame22therebetween to side-shift the draft frame22and circle frame24, and thus the moldboard20, relative to the main frame18. The tilt cylinder29is connected to the circle frame24and the tilt frame28therebetween to change the pitch of the tilt frame28, and thus the moldboard20, relative to the circle frame24. A moldboard side-shift cylinder36is connected to the tilt frame28and the moldboard20therebetween and is operable to move the moldboard20in translation relative to the tilt frame28along a longitudinal axis of the moldboard20.

Referring toFIG. 3, the circle drive26is configured to rotate the circle gear25and thus the moldboard20relative to the draft frame22about the central axis of the circle gear25. In this embodiment, the circle drive26has a dual-worm circle drive gearbox27. The gearbox27has gearing38, a first worm40, and a second worm40. The gearing27meshes with the circle gear25. The first and second worms40mesh with the gearing27. The gearbox27may have, a number of mounting pads41extending outwardly from a housing60of the gearbox and fastened (e.g., using threaded fasteners) to the draft frame22. There may be, for example, three such mounting pads41.

Exemplarily, the gearing38includes a worm gear42and a pinion gear44. The first and second worms40mesh with the worm gear42. The worm gear42is operatively coupled to the pinion gear44. The pinion gear44meshes with the circle gear25. Each worm40may be made, for example, of hardened steel, and the worm gear42may be made, for example, of high-strength manganese bronze.

In the illustrated embodiment, the worms40are positioned on opposite sides of the worm gear42so as to be parallel, and are oriented to point in the same direction. The worms40are threaded with opposite senses. Such a configuration of the worms40facilitates packaging of the worms40and the motors48coupled respectively thereto on board the vehicle10. Positioning the worms40on opposite sides of the worm gear42may help counter-balance the bearings66of the gearbox27.

To facilitate other packaging arrangements, the worms40may be arranged in a variety of ways. For example, the worms40may be parallel to one another but oriented 180 degrees to one another, in which case the worms40may be threaded with the same sense, and the motors48may be positioned on opposite sides of the gearbox27. In other examples, the worms40may be angled relative to one another in a generally V-shaped arrangement, the angle of the V shape dependent on packaging constraints and possibly the location of any mounting pads41about the housing60of the gearbox27. In such a case, both of the motor ends of the worms40(i.e., the ends coupled to the motors48) may be positioned toward the vertex of the V shape or may be positioned away from the vertex of the V shape, or one of the motor ends may be positioned toward the vertex with the other motor end positioned away from the vertex.

Referring toFIG. 4, the circle drive26further includes a hydraulic system46configured to rotate the first and second worms40. The hydraulic system46includes a hydraulic first motor48and a hydraulic second motor48. The first and second motors48are flow-parallel to one another and are operatively coupled respectively to the first and second worms40to rotate the worms40. Due to the flow-parallel arrangement, the circle drive26is able to self-balance such that the first and second motors48produce the same or similar motor torque as one another, with the worms40applying corresponding torque to the worm gear42and rotating so as to avoid seizure of the worm gear42. The motors48may not produce exactly the same torque as one another; rather the motor torques may be slightly different (e.g., up to 5% difference).

Assume, for example, that just before start-up of the gearbox27the thread of one of the worms40(the “ready worm”) is positioned between adjacent teeth of the worm gear42(a lead tooth and a trailing tooth) such that the thread is contacting the forward flank of the lead tooth so as to be ready to apply torque to the worm gear42in a forward direction, whereas the thread of the other worm40(the “other worm”) positioned between adjacent teeth (a lead tooth and a trailing tooth) is spaced slightly apart from the forward flank of the lead tooth so as not to be ready to apply torque to the worm gear42in the forward direction (“misalignment”). In the case of such misalignment, the flow-parallel arrangement will send flow to the side with the other worm40(i.e., that the side with least resistance) in order to rotate its thread into contact with the respective forward flank, while the ready worm40waits momentarily. During this initial stage, the rotational speed of the worms40may be unequal and the torque applied by the worms40may be low. The rotational speeds of the worms40equalize and the torque applied by the worms40rises in response to engagement by the other worm40with the respective forward flank. The flow-parallel arrangement thus naturally accommodates manufacturing tolerances and thread-tooth spacing between the worms40and worm gear42that may occur due to slight rotational shifting between the worms40and worm gear42during periods of circle drive inactivity.

The hydraulic system46has a hydraulic circuit50coupled fluidly to the motors48. The hydraulic circuit50supplies pressurized hydraulic fluid to the motors48and receives return fluid from the motors48. The circuit50can supply fluid in a direction to rotate the circle frame24and the moldboard20in a corresponding direction and supply fluid in an opposite direction to rotate the circle frame24and the moldboard20in a corresponding opposite direction.

The hydraulic circuit50may be configured in a variety of ways. For example, the circuit50may be a pressure-compensated, load-sense arrangement that serves a plurality of hydraulic functions, including the circle-rotate function. As such, it may have a pump (e.g., variable displacement or fixed displacement) for supplying pressurized hydraulic fluid to the functions and a reservoir for storing hydraulic fluid. It may have proportional directional control valves associated respectively with the functions and proportional compensator valves associated respectively with the functions. The directional control valves may include a directional control valve for controlling flow between the pump and the motors48and between the motors48and the reservoir, as well as the direction of such flow. The directional control valve may be, for example, manually operable or pilot operable. In the case of manually operable, the directional control valve may be coupled mechanically to a circle-rotate control (e.g., lever) at the operator's station. In the case of pilot operable, there may be two electro-hydraulic proportional pilot valves for controlling pilot flow to opposite ends of the control valve. The pilot valves may be under the control of an electric control unit, having one or more electric controllers, responsive to operator inputs via a circle-rotate control (e.g., lever) at the operators station.

The hydraulic motors48may be configured in any suitable manner. In an example, each hydraulic motor48is a gerotor motor, such as, for example an Eaton 2000 series gerotor motor from Eaton Corporation of Cleveland, Ohio [e.g., with a specification of M-02-062-BE-05-AA-01-0-00-1-0-00-00-00-AB-AC-F having a displacement of 6.2 cubic inches per revolution (i.e., about 100 cubic centimeters/revolution), a BE mounting type, and a SAE size A mounting flange to be fastened to the mounting flange of a connector74of the gearbox27]. In other examples, each motor48may be an axial piston motor or a gear motor.

The gearbox27may be configured with a slip clutch, as shown, for example, inFIG. 5or without a slip clutch. The slip clutch protects, for example, the moldboard20, circle frame24, gearbox27, and draft frame22from damage if the end of the moldboard20comes in contact with stationary, immovable objects.

Referring toFIG. 5, the gearbox27with the slip clutch, in the form of a wet slip clutch, is shown and is but one possible arrangement of a gearbox with a slip clutch. The gearbox27has a housing60. The housing60includes a base61, a cover62fastened to the base61using screws, and a cap63fastened to the cover using screws (two of such screws shown in section inFIG. 5in which the threads of the screws and the corresponding threads of the holes receiving the screws are not shown for ease of illustration).

Each motor48is coupled mechanically to the gearbox27. The motor48has a housing fastened to the gearbox housing60. For example, the housing of each motor48has a mounting flange fastened (e.g., using two bolts and associated nuts and washers) to the mounting flange of a connector74of the housing60, such connector74being fastened (e.g., using screws) to the base61. The mounting flanges of the motors48and the connectors74may each be configured as an SAE size A mounting flange. The output shaft of the motor48is coupled mechanically to the worm40. An end cap76is fastened (e.g., using screws) to the base61opposite the mounting flange74.

The worms40and the worm gear42are positioned within the housing60. Each worm40is positioned within the base61and is rotatable within a pair of tapered roller bearings (FIG. 3) captured respectively between the worm40and a mounting flange74and between the worm40and an end cap76. The worms40mesh with the worm gear42which is positioned within the housing60between the base61and the cover62with a thrust washer positioned between the worm gear42and the base61and another thrust washer positioned between the worm gear42and the cover62for rotation of the worm gear42within the housing60.

A clutch pack64is positioned radially between the worm gear42and an annular hub65splined to a shaft of the pinion gear44. The clutch pack64has separator plates and clutch disks inter-digitating with the separator plates in frictional engagement therewith. The separator plates are splined to the worm gear42. The clutch disks are splined to the hub65, and each disk may have a core plate with frictional paper (not shown) on both sides of the plate.

The shaft of the pinion gear44is mounted for rotation within a pair of tapered thrust bearings66. A retaining washer68is fastened to the shaft of the pinion gear44with a first set of screws (e.g., three screws) and is shimmed with a first set of shims between the washer68and a quill bearing70to establish a pre-load on the upper bearing66. The quill bearing70is fastened to the shaft of the pinion gear44with a second set of screws (e.g., three screws) and is shimmed with a second set of shims between the quill bearing70and the end of that shaft to establish a pre-load on a spring72(e.g., Belleville spring).

The spring pre-load is transmitted to the clutch pack64via a pressure plate and a wear plate. The pressure plate engages the spring72on one side and engages the hub65and a wear plate on the other side. The wear plate is sandwiched between the pressure plate and the clutch pack64.

On the other side of the clutch pack64is a backing plate. The backing plate engages the hub65and the clutch pack64on one side and engages one of the bearings66on the other side.

The spring pre-load normally causes engagement of the clutch pack64such that there is no slip between the worm gear42and the pinion gear44. In the event that the spring pre-load is overcome due, for example, to an obstacle to rotation of the circle gear25, the clutch pack64may slip allowing the worm gear42to rotate ahead of the pinion gear44.

The interior of the housing60, including the worm gear set with its worms40and worm gear42, is lubricated with hydraulic oil or other suitable lubricant. Seals are provided, for example, between the cap63and the cover62(e.g., rubber O-ring), between the cover62and the base61(e.g., rubber O-ring truncated for ease of illustration to indicate compression during use), and between the base61and the pinion gear44(e.g., rubber ring). The housing60may be provided with a pressure relief valve.

The gearbox27may be configured without a clutch pack and associated components. In but one possible arrangement of such a clutchless gearbox, the gearbox has a housing including a base, a cover fastened to the base using screws, and a cap secured to the base (e.g., pressed into the cover).

Each motor48is coupled mechanically to the clutchless gearbox. The motor has a housing fastened to the gearbox housing. For example, the housing of each motor is fastened (e.g., using threaded fasteners) to a mounting flange of the gearbox housing which is fastened (e.g., using threaded fasteners) to the base. The output shaft of the motor is coupled mechanically to the worm. An end cap is fastened (e.g., using threaded fasteners) to the base opposite the mounting flange.

The worms and the worm gear are positioned within the housing60of the clutchless gearbox. Each worm is positioned within the base and is rotatable within a pair of tapered roller bearings captured respectively between the worm and one of the mounting flanges and between the worm and one of the end caps. The worms mesh with the worm gear which is positioned within the housing between the base and the cover with a thrust washer positioned between the worm gear and the base and another thrust washer positioned between the worm gear and the cover for rotation of the worm gear within the housing.

In the clutchless gearbox, the shaft of the pinion gear is mounted for rotation within a pair of tapered thrust bearings. A retaining washer is fastened to the shaft of the pinion gear with a set of screws (e.g., three screws) and is shimmed with a set of shims between the retaining washer and an end of the shaft to establish a pre-load on the upper bearing.

The interior of the housing of the clutchless gearbox, including the worm gear set with its worms40and worm gear42, is lubricated with hydraulic oil or other suitable lubricant. Seals are provided, for example, between the cover and the base (e.g., rubber O-ring), and between the base and the pinion gear (e.g., rubber ring). The housing may be provided with a pressure relief valve.

It is understood that the gearing38may take the form of any suitable gearing between the worms40and the circle gear25that is configured to transmit torque inputted by the worms40to the circle gear25. It is preferred that the gearing38include a single worm gear42with which the worms40mesh, but it is understood that there could be two worm gears, one for each worm, operatively coupled to the same pinion gear (in the event that there are more than two worms, there could be more than two worm gears, each worm gear for one or more worms). The clutch and clutchless embodiments of the connection between the worm gear42and the pinion gear44are but two examples of such connection. Further, the pinion gear44may take the form of any suitable pinion gear that is configured to transmit torque imparted to it to the circle gear25.

In use, there may be a circle-rotate control (e.g., a lever) at the operator's station16. An operator may actuate the circle-rotate control (e.g., move lever selectively fore or aft relative to a neutral position) to rotate selectively the moldboard20clockwise or counter-clockwise about the central axis of the circle gear25. Actuation of the circle-rotate control causes pressurized fluid to advance to the two motors48in the direction corresponding to the direction of actuation of the circle-rotate control. In response thereto, the first motor48drives the first worm40and the second motor48drives the second worm40, such that the first and second worms drive the gearing38, or more particularly the worm gear42of the gearing38. As such, the motors48rotate respectively the worms40which rotate the worm gear42, the pinion gear44, and thus the circle gear25and the moldboard20coupled thereto.

The circle drive26is configured to divide the overall torque (T) applied to the gearing38among the multiple worms40. Each of the worms40applies a portion of the overall torque (T) to the worm gear42. For example, in the case of a gearbox27with only two worms40, the first worm40applies approximately ½ (T) to the worm gear42, and the second worm40applies approximately ½ (T) to the worm gear42.

The gearbox27thus has multiple worms40. It is thought that use of multiple worms40will decrease the wear rate on the worm gear42so as to lengthen its useful life. As in the illustrated embodiment, the gearbox27may have only two worms40. In other embodiments, the gearbox27may have more than two worms (e.g., three, or more), further dividing the torque applied by each worm40to the worm gear42.

The motors may be the same in number as the worms. For example, in the case of two worms, there may be two motors operatively coupled respectively to the two worms. In the case of three worms, there may be three motors operatively coupled respectively to the three worms, and so on. The worms and, correspondingly, the motors may be spaced apart evenly about the gearbox, such as, for example, 180 degrees in the case of two worms and two motors or 120 degrees in the case of three worms and three motors.

The circle drive26may be configured in a number of ways. For example, as alluded to above, the worms40may be driven hydraulically. In another example, the worms40may be driven pneumatically using two pneumatic motors operatively coupled respectively to the two worms40and arranged in flow-parallel in lieu of the hydraulic motors. As such, the pneumatic motors may produce the same or similar motor torque as one another such that the worms40apply torque correspondingly to the worm gear42. The pneumatic motors may not produce exactly the same torque as one another; rather the motor torques may be slightly different (e.g., up to 5% difference).

In yet another example, electric motors may be used in place of hydraulic or pneumatic motors. As such, there may be two electric motors operatively coupled respectively to the two worms40. The electric motors may be controlled so as to produce the same or similar motor torque as one another such that the worms40apply torque correspondingly to the worm gear42. The electric motors may not produce exactly the same torque as one another; rather the motor torques may be slightly different (e.g., up to 5% difference).

A suitable motor control system may be used for the electric motors. For example, the control system monitors the torque of the motors and applies a predetermined upper torque limit to the motors such that, if the torque of only one of the motors reaches the upper torque limit indicating that the thread of the worm40to which such motor is coupled is contacting the respective forward flank of the worm gear42but the thread of the other worm40is not contacting the respective forward flank of the worm gear42, the motor control system causes the output shaft of the other motor to rotate so that the thread of the worm40coupled thereto contacts the respective forward flank. Motor torque can be sensed in any of several ways. For example, motor torque can be sensed by monitoring the motor current. As monitored motor current increases, the torque increases.

Referring toFIG. 6, in yet another example, the circle drive26may have a single motor148(e.g., hydraulic, pneumatic, or electric) coupled mechanically to each worm40(a single hydraulic motor may be driven by the hydraulic circuit50). In the case of two worms, the output shaft of the single motor48is coupled to both worms40via a differential52(e.g., open differential), which transmits the same or similar torque to the worms40while allowing for rotational speed variation between the worms40until both worms40engage the respective forward flanks (e.g., at start-up of the gearbox). The torque applied to the two worms40may not be exactly the same; rather the torques may be slightly different (e.g., up to 5% difference).

Referring toFIG. 7, in a variation of the embodiment ofFIG. 6, there may be a gearbox80in lieu of a differential. The gearbox80may have an input82configured, for example, as a shaft coupled mechanically to the motor148such that the motor148is operatively coupled to the gearbox80. The gearbox80may have two input gears84on the input82to rotate therewith. The gears84are coupled mechanically respectively to two output gears85. The output gears85are coupled mechanically respectively to two outputs86of the gearbox80. The outputs86are coupled mechanically respectively to the first and second worms40.

To avoid seizure of the worm gear42, one of the outputs86may be a multi-shaft output having two shafts87and an adjustable coupling88that couples the shafts87to one another and is configured to allow relative rotation between the two shafts87during set-up, while the other output86may be a single shaft rigidly coupled to the respective worm40. In particular, prior to set-up, one or both of the worms40may not be positioned against the respective forward flanks of the worm gear42.

To correct such misalignment, during set-up, the adjustable coupling88may be made loose so as to allow relative rotation between the two shafts87of the multi-shaft output86, and, if needed, the single shaft of the single-shaft output86may be rotated so as to cause the associated worm40to engage the respective forward flank of the worm gear42. Further, if needed, the shafts87of the multi-shaft output86may be individually rotated. The shaft87connected to the gearbox27may be rotated so as to cause the associated worm40to engage the respective forward flank of the worm gear42. In addition, the shaft87connected to the gearbox80may be rotated so as to cause the gearing of the gearbox80to mesh properly. Afterwards, the adjustable coupling88may be tightened to connect the shafts87of the multi-shaft output86rigidly.

Referring toFIGS. 8 and 9, there is shown a first embodiment188of the adjustable coupling88. The adjustable coupling188has a flange190at an end of each of the shafts87. The two flanges190are joined to one another with fasteners192(e.g., socket head cap screws). The fasteners192extend respectively through threaded circular holes194in one of the flanges190(left flange ofFIG. 9), whereas the other flange190(right flange ofFIG. 9) has arcuate, elongated, slots196through which the fasteners192extend respectively.

During set-up, the fasteners192may be positioned in the slots196and the holes194but made loose so as to allow relative rotation between the two shafts87of the multi-shaft output86to correct misalignment in either gearbox27,80, and then tightened after any misalignment is corrected. When the fasteners192are tightened, a male frusto-conical portion of one of the shafts87(e.g., right shaft ofFIG. 9) engages a female frusto-conical portion of the other shaft87(e.g., left shaft ofFIG. 9). Alternatively, in lieu of the flanges190and the fasteners192, there may be a single threaded fastener (e.g., cap screw) that extends through an unthreaded through-hole in one of the shafts87(e.g., the left shaft ofFIG. 9) into a blind threaded hole in the other shaft87(e.g., the right shaft ofFIG. 9) to connect the two shafts87together.

Referring toFIGS. 10 and 11, there is shown a second embodiment288of the adjustable coupling88. The adjustable coupling288has a flange290at an end of each of the shafts87. Each of the two flanges290has two sets of two threaded circular holes294and two arcuate; elongated slots296. The two sets of holes294are positioned diametrically opposite one another, and the two slots296are positioned diametrically opposite one another, such that the two sets of holes294and the two slots296alternate with one another circumferentially about the flange290. The two flanges290are joined to one another with fasteners292(e.g., sockets head cap screws). There are two fasteners292extending through each slot296of each flange290into respective holes294of the other flange290. Each fastener292abuts a recessed shoulder298of the slot296through which it extends. During set-up, the fasteners292may be positioned in the slots296and the holes294but made loose so as to allow relative rotation between the two shafts87of the multi-shaft output86to correct misalignment in either gearbox27,80, and then tightened after any misalignment is corrected.

In lieu of a motor, the worms40may be driven mechanically through a drive line from the engine or the transmission. The drive line may be coupled to the two worms40via a differential.

The gearbox27may have a slip clutch or be clutchless with any of the foregoing variations of the circle drive26.