GB2493961A - Power takeoff drive system for an agricultural tractor - Google Patents

Abstract

A power takeoff drive system 10 for an agricultural tractor with an epicyclic gear arrangement 20 comprises a first epicyclic gear element 21 which is selectively coupled to one of an engine and a brake 44. A second epicyclic gear element 30 is coupled to an auxiliary motor. A third epicyclic gear element 24 is coupled to a power takeoff output shaft 26. The system is operable in a starting mode in which torque to drive the output shaft is derived from the auxiliary motor. In a hybrid mode the epicyclic gear arrangement sums the power delivered by the engine and the auxiliary motor. A continuously variable drive ratio is thereby provided for the power takeoff.

Description

DESCRIPTION

POWER TAKEOFF DRIVE SYSTEM FOR AN AGRICULTURAL TRACTOR

[01] The invention relates to power takeoff (PTO) drive systems for agricultural tractors.

[023 For many years agricultural tractors have been fitted with PTO systems which allow the transfer of torque from the prime mover to an attached implement.

Examples of implements that utilise PTO systems include balers, fertilizer spreaders, seed drills and hedge cutters to name but a few.

[03] Some implements, tillage implements for example, are power hungry and place a constant high load upon the PTO typically operating at the nominal engine speed to deliver the optimum efficiency. Other implements such as fertilizers spreaders place a low load upon the PTO but still demand the maximum speed. The demanded PTO speed dictates the speed at which the engine must be run due to the direct mechanical connection between the engine and the output PTO stub,. In the case of low load at applications this results in excessive fuel consumption and noise.

[04] Some implements demand a constant ratio between the groundspeed and the PTO speed. Some tractors provide a groundspeed PTO mode wherein the propulsion drive to the wheels is directly coupled by meshed gears to the PTO stub.

Unfortunately the ratio between groundspeed and PTO speed in such a mode is fixed by the gears installed during manufacture and the size of tyre fitted.

[05] Some trailers are designed to exploit groundspeed PTO wherein torque is drawn from the tractor to drive wheels of the trailer. However, such trailers cannot be freely changed between tractors unless their groundspeed PTO drive ratios are matched. Some trailer manufactures have proposed hydraulically driven axles to overcome this drawback of groundspeed PTO drive. The extra components however add extra weight and cost to the trailer design.

[06] Balers and the like demand a high torque upon start-up due to a heavy flywheel on the baler which initially absorbs energy. Often this spike in power consumption can lead to clutch damage, engine stall or breaking of a shear bolt.

[07] International patent application number WO-201 1/054656 in the name of the applicant discloses a PlO system having an in-line clutch to disengage the direct mechanical drive connection between a prime mover and the output PlO stub. This allows, in a hydraulic mode, a hydraulic motor to drive the PlO stub, the speed of which can be varied independently of the speed of the prime mover. Although this addresses the problems mentioned above in relation to fixed drive ratios, the disclosed system can still only deliver a tixed drive ratio between the prime mover and RIO at high loads.

[08] It is an object of the invention to provide a PTO drive system for an agricultural tractor which at least alleviates some the aforementioned problems.

[09] In accordance with a first aspect of the invention there is provided a power takeoff drive system for an agricultural tractor comprising an epicyclic gear arrangement having a first epicyclic gear element which is selectively coupled to one of an engine and a brake, a second epicyclic gear element coupled to an auxiliary motor, and a third epicyclic gear element coupled to a power takeoff output shaft.

The provision of an epicyclic gear arrangement allows the summing of power delivered by: (a) a prime mover and (b) an auxiliary motor. The speed relationship between the engine and the PTO shaft can, therefore, be adjusted by the auxiliary motor.

[10] In other words, a hybrid power source is provided for the PlO shaft wherein power is drawn from both the engine and the auxiliary motor.

[11] The drive system is preferably operable in a first hybrid' mode wherein the first epicyclic element is coupled to the engine, and in a second start up' mode wherein the first epicyclic element is coupled to the brake. In the hybrid mode the PTO is driven by the engine and the auxiliary motor, whereas in the start up mode the power for the PlO shaft is derived solely from the auxiliary motor Advantageously, by decoupling the epicyclic gear arrangement from the engine, the auxiliary motor can be used alone to initiate drive to the PTO output shaft thereby delivering a high torque at low speed. This is particularly beneficial to the starting of implements which present high inertia due to heavy flywheels for example.

[12] The drive system may be operable in a third neutral' mode in which the first epicyclic gear element is decoupled from both the engine and the brake.

Advantageously, the neutral mode allows free running of the FTO shaft and can be activated when drive thereto is disengaged. This leaves the residue inertia to subside through frictional forces and avoids stress placed upon the drive system.

[13] In a preferred arrangement the first epicyclic gear element is a sun gear.

This permits simple construction of the coupling mechanism between the epicyclic gear arrangement and the engine. The second epicyclic gear element is preferably a planet carrier and wherein the third gear element comprises ring gear meshed with planetary gears supported on the planet carrier.

[14] The auxiliary motor is preferably an electric motor so that high torques can be delivered at relatively low speeds and can operate at a wide range of speeds.

Alternatively, the auxiliary motor may be a hydraulic motor.

[15] The engine, for example an internal combustion engine, is preferably coupled to the first epicyclic element via a step-up gear arrangement which delivers an input-to-output speed ratio of less than 1, more preferably less than 0.5.

[16] The step-up gear arrangement may comprise an output element coupled to the first epicyclic gear element by a shaft which powers a generator. The eiectrical energy generated by such a generator is, in a preferred arrangement, utilised to power an electrical auxiliary motor coupled to the second epicyclic gear element.

Advantageously, in this case, the power to drive the PTO shaft is a hybrid of power derived directly from the engine and power derived indirectly by conversion to electrical energy. The variable engine-to-PTO speed ratio allows for more efficient power generation by the engine, for example by running at constant speed.

[17] The step-up gear arrangement may comprise a second epicyclic gear arrangement comprising a sun gear coupled to the first epicylic element and a planet carrier coupled to the engine. This provides an efficient mechanism to step up the speed desired for driving the generator.

[18] In accordance with a second aspect of the invention there is provided a method of operating a PlO drive system as described above comprising the steps of coupling the first epicyclic gear element to the brake, then starting the auxiliary motor to initiate rotation of the power takeoff output shaft. As described above this offers a mode of operation which is particularly advantageous for heavy implements such as balers and avoids the risk of stalling the engine or causing damage to the clutch.

[19] The method may further comprise the step of simultaneously decoupling the first epicyclic gear element from the brake, coupling the first epicyclic gear element to the engine, and reducing the speed of the auxiliary motor to maintain a substantially constant speed of the PTO output shaft. It is recognised that the maximum power cannot be delivered to the PTO shaft by electrical energy alone for a sustained period. At an engaging speed ratio' a hybrid mode must be initiated.

[20] It will be appreciated that software controlling the various clutches involved will have stored therein various parameters to determine the point at which the PTO drive is switched from solely electrical to hybrid.

[21] The speed of the PTO output shaft may be controlled by varying the auxiliary motor speed whilst keeping the engine speed substantially constant.

Advantageously, this allows the engine to be run with optimal efficiency. Surplus power is exploited to create electrical energy which may be stored by batteries or used to power propulsion in the case of electrically-propelled vehicles. Alternatively.

in another mode, the PTO shaft speed is kept constant. Variations in the engine speed are catered for by appropriate controi of the auxiliary motor speed.

[22] The PTO output shaft may be deactivated by several different methods. In a first deactivation method the first epicyclic gear element is decoupled from both the brake and the engine so that it can turn freely. In an alternative method the auxiliary motor speed is reduced so as to reduce the speed of the PTO output shaft before decoupling from the power source. In this case the first epicyclic element may be coupled to the brake at a predetermined speed.

[23] In one mode of operation the PTO output shaft is driven in reverse by coupling the first epicyclic gear element to the brake and operating the auxiliary motor in reversa This provides the operator with a means of reversing the PTO at a controlled speed to unblock a jammed implement for example.

[24] Further advantages of the invention will become apparent from reading the following description of specific embodiments with reference to the appended drawings in which:-Figurel shows a vertical section through a PTO drive system in accordance with an embodiment of the invention; Figure 2 is an enlarged view part of the drive system of Figure 1; Figures 3, 4 and 5 are schematic views representing the drive system of Figure 1 showing the start-up mode, hybrid mode, and neutral mode respectively.

[25] Specific aspects and constructional features of the invention will now be described by way of example. Relative terms such as front', rear', longitudinal' and transverse' are used with reference to the normal forward direction of travel of the tractor in which the example FTC drive system is embodied.

[26] With reference to Figure 1, a PTO drive system 10 is installed in an agricultural tractor (not shown). Although not critical to the principles of the invention, the drive system 10 is enclosed within the housing of a transaxle which is coupled to an engine housing in the normal manner. Figures 1 to 5 are viewed from the left-hand side of the tractor wherein the engine (not shown) is connected to the left-hand side of the drawings and an implement is coupled to the tractor on the right-hand side of the drawing.

[27] The engine, which may be an internal combustion engine or an electric motor, has an output drive shaft which is drivingly coupled to a flywheel 12 as is common in existing agricultural tractors. The flywheel 12 comprises an integrated planet carrier 13 upon which three planet gears 14 (only one is shown in Figure 1) are mounted for rotation. Each planet gear 14 is meshed with, and orbits around, a sun gear 15 which is keyed onto an end of a driveshaft 16. It will be appreciated that all rotational components including the epicyclic elements 13, 14, 15, and drive shafi 16 rotate around respective axes that are aligned longitudinally with respect to the tractor.

[28] Planet carrier 13, planet gears 14, and sun gear 15 together provide a step-up gear arrangement which generates an engine speed-to-driveshaft speed ratio of 1 to 4 so that an engine speed of 1500rpm translates to a rotational speed of 6000rpm for drive shaft 16. It will of course be appreciated that the gearing may be modified to provide different gear ratios.

[29] Associated with driveshaft 16 is an electrical generator 17 which is shown schematically only in the drawings. Rotational mechanical energy of driveshaft 16 is converted into electrical energy by generator 17 which is subsequently stored in batteries (not shown) or utilised by the auxiliary motor 18 to be described below. It will be understood that the various electrical connections required for generator 17 and auxiliary motor 18 are not shown.

[303 Turning to Figure 2, the RIO system 10 includes an epicyclic gear arrangement 20 having a sun gear 21 which is selectively coupled to driveshaft 16 by a multi-plate clutch 22. Activation of clutch 22 is done hydraulically by the application of pressurised hydraulic fluid through a port 22a. Sun gear 21 can, therefore, be selectively coupled and decoupled from driveshaft 16 by appropriate application of hydraulic signals to clutch 22.

[31] Epicyclic unit 20 further comprises a planet carrier 24 which supports three compound planet gears 25 for orbital motion around sun gear 21. Planet carrier 24 is keyed onto PlO output shaft 26 so that the two components rotate in unison.

Bearings 27 support planet carrier 24 for rotational movement within frame member 28.

[32] The epicyclic arrangement 20 further comprises a drum 30 which includes ring gear 31 on the inside surface thereof. The three planet gears 25 mesh with both the ring gear 31 and sun gear 21. Drum 30 is mounted for rotational movement within frame member 28 by a pair of bearings 32.

[33] Drum 30 includes an integrated exterior annulus gear 34 which meshes with gear 35 which is integrated with countershaft 36. Bearings 37 support countershaft 36 for rotational movement upon a frame member (not shown).

13] Electrical motor 18 comprises an output shaft 38 which is drivingly coupled to countershaft 36 by respectively keyed gears 39, 40 provided on those shafts 38, 36. Motor output shaft 38 is supported for rotation within a frame by bearing 42.

Therefore, the output of motor 18 is drivingly coupled to drum 30 by a direct mechanical connection.

[35] Turning back to sun gear 21, a second multi disc clutch 44 is provided to selectively couple hub member 21a to a frame member 48 so as to provide a brake for the sun gear 21 which can be selectively applied by the application of hydraulic signals applied to port 44a. It should be understood that frame members 28 and 48 are fixed in relation to the chassis of the tractor so that application of the sun gear brake delivers a retarding force thereto.

[36] Operation of the PlO drive system 10 will now be described with reference to Figures 3, 4 and 5 which each represent different modes of operation of the specific construction described above.

[37] It will be understood that the input variables for operation of the system includes speed of the engine, speed of the electrical motor 18, opening and closing of first clutch 22 and opening and closing of brake clutch 44. The result in output variable is the speed and talk of PTO output shaft 26 which is coupled to an attached implement.

Starting Mode (Figure 3) [38] When not activated the PTO shaft 26 is held stationary by closing brake clutch 44 and opening first clutch 22. Furthermore, the speed of electrical motor 18 is zero. The closing of brake clutch 44 effectively connects sun gear 21 to the tractor frame 48 whilst the opening of first clutch 22 decouples the engine drive from the PlO drive system 10.

[39] Upon receipt of start up command from an operator (via a user interface), a controller (not shown) increases the output speed of motor 18 from zero. Torque derived from motor 18 is conveyed to PTO shaft 26 via the drive train provided by countershaft 38 drum 30 and planet carrier 24.

[40] Electrical motors are capable of delivering higher torques at low speed for short periods and so the system disclosed lends itself particularly well to initiating the drive of heavy implements such as balers and toppers which carry a high inertia. This reduces the number of broken shear bolts and generally reduces stress placed upon the drive line.

[41] The start up mode can also be employed for low load applications wherein the torque used to drive the implement is derived solely from the motor 18. The motor output can be controlled accordingly to achieve the desired speed of the PTO output independent of the engine speed. Such low load implements include fertilizer spreaders for example.

Hybrid Mode (Figure 4) [423 At higher loads the hybrid mode is initiated, preferably automatically, wherein the first clutch 22 is closed and the brake clutch 44 is opened simultaneously. At the same time the controller (not shown) reduces the output speed of motor 18 to smooth the transition between start up mode and hybrid mode and avoid a step increase in the output speed of P10 shaft 26.

[43] In the hybrid mode the speed of motor 18 is controlled in conjunction with the engine speed to deliver the desired output speed of PTO shaft 26. Although not shown in the drawings a controller may sense the output speed of the engine to calculate the required speed of motor 18 to achieve the desired output speed. In one example method of operation a steady P10 output speed is required independent of engine speed and ground speed. In this case the speed of motor 18 is reguiated to achieve a constant PTO output speed.

[44] In a second example method of operation a fixed ratio between the groundspeed and the PTO output speed is commanded (equivalent to existing groundspeed FTC modes today). In this case a controller may sense the groundspeed directly or indirectly via sensors measuring the engine speed and propulsion drive ratio to allow calculation (using embedded algorithms) to obtain the required motor speed in real time.

[45] In a third example method of operation the PTO-to-engine speed ratio is kept constant as in standard PTO systems existing today. In this case the motor speed is kept substantially constant to allow a direct drive relationship between the engine and P10 shaft 26. Of course, upon command by the driver, or automatically by a control system, this ratio may be varied by changing the speed motor 18.

[46] In all cases the hybrid mode of operation may be regulated by the control algorithms to optimise the efficiency of the engine and avoid wasted power. Control of the PTO system 10 may be executed by many different algorithms which can be

S

envisaged by a person skilled in the alt and further details need not be disclosed herein. It will be appreciated that control of the P10 speed may also take into account the groundspeed of the tractor in addition to the transmission propulsion ratio.

Disengagement (Figure 5) [47] The drive to the PTO shaft 26 may be disengaged by opening both clutches 22, 44, and reducing the motor speed to zero. This neutral mode' allows the inertia of the attached implement to dissipate slowly thus minimising stresses placed upon the driveline. Furthermore, the neutral mode allows for free rotation of the PTO output shaft 26 and is particularly useful when attaching an implement so that the operator can conveniently align the splines on the PTO shaft.

[48] In an alternative method of stopping the PlO drive, first clutch 22 is opened whilst braking clutch 44 is closed (maybe gradually) and wherein the speed of PTO shaft 26 is slowed by appropriate control of motor 18 down to zero.

[49] The method of disengaging the P10 drive may be selected manualiy by a driver or automatically by a control system.

Reversing the PTO Output [50] With the brake clutch 48 closed and the first clutch 22 open (as shown in Figure 3), the motor 18 may be driven in reverse in a controlled manner to reverse the P10 output shaft 26. Such a mode has useful application when attempting to unblock a jammed implement. Appropriate warnings to the driver should be provided when implementing such a mode as reversing some implements may cause damage thereto.

[51] Although the motor 18 described above is powered electrically, it is envisaged that other auxiliary motors maybe employed without deviating from the scope of the invention. For example, hydraulic motors powered by hydraulic pumps may instead be employed.

[52] Furthermore, it should be understood that the specific epicyclic elements of the epicyclic arrangement 20 may be interchanged with appropriate changes to the motor control without deviating from the scope of invention. For example, the driveshaft 16 maybe selectively coupled to the planet carrier whilst the PTO output shaft 26 is coupled to a sun gear. Other alternatives will be envisaged by those skilled in the art.

[53] In summary, a power takeoff drive system for an agricultural tractor is provided. An epicyclic gear arrangement comprises a first epicyclic gear element which is selectively coupled to one of an engine and a brake. A second epicyclic gear element is coupled to an auxiliary motor. A third epicyclic gear element is coupled to a power takeoff output shaft. The system is operable in a starting mode in which torque to drive the output shaft is derived from the auxiliary motor. In a hybrid mode the epicyclic gear arrangement sums the power delivered by the engine and the auxiliary motor. A continuously variable drive ratio is thereby provided for the power takeoff.

Claims (1)

1. <claim-text>CLAIMS1. A power takeoff drive system for an agricultural tractor, comprising an epicyclic gear arrangement having a first epicyclic gear element which is selectively coupled to one of an engine and a brake, a second epicyclic gear element coupled to an auxiliary motor, and a third epicyclic gear element coupled to a power takeoff output shaft.</claim-text> <claim-text>2. A drive system according to Claim 1, operable in a first, hybrid, mode wherein the first epicyclic element is coupled to the engine, and in a second, start-up, mode wherein the first epicyclic element is coupled to the brake.</claim-text> <claim-text>3. A drive system according to Claim 2, operable in a third, neutral, mode in which the first epicyclic gear element is decoupled from both the engine and the brake.</claim-text> <claim-text>4. A drive system according to any preceeding claim, wherein the first epicyclic gear element is a sun gear.</claim-text> <claim-text>5. A drive system according to Claim 4, wherein the second epicyclic gear element is a planet carrier and the third gear element comprises ring gear meshed with planetary gears supported on the planet carrier.</claim-text> <claim-text>6. A drive system according to any preceding claim, wherein the auxiliary motor is an electric motor.</claim-text> <claim-text>7. A drive system according to any preceding claim, wherein the auxiliary motor is a hydraulic motor.</claim-text> <claim-text>8. A drive system according to any preceding claim, wherein the engine is coupled to the first epicyclic element via a step-up gear arrangement which delivers an input to output speed ratio of less than 1.</claim-text> <claim-text>9. A drive system according to Claim 8, wherein the step-up gear arrangement comprises an output element coupled to the first epicyclic gear element by a shaft which powers a generator.</claim-text> <claim-text>10. A drive system according to Claim 9 and 6, wherein electrical energy generated by the generator is utilised to power the electrical motor.</claim-text> <claim-text>11. A drive system according to any one of Claims 8, 9 or 10, wherein the step-up gear arrangement comprises a second epicyclic gear arrangement.</claim-text> <claim-text>12. A drive system according to Claim 11, wherein the second epicyclic gear arrangenient comprises a sun gear coupled to the first epicyclic element, and a planet carrier coupled to the engine.</claim-text> <claim-text>13. A method of operating a power takeoff drive system according to any preceeding claim, comprising the steps of: -coupling the first epicyclic gear element to the brake; -then starting the auxiliary motor to initiate rotation of the power takeoff output shaft.</claim-text> <claim-text>14. A method according to Claim 13, further comprising the step of simultaneously: -decoupling the first epicyclic gear element from the brake; -coupling the first epicyclic gear element to the engine; and, -reducing the speed of the auxiliary motor to maintain a substantially constant speed of the power takeoff output shaft.</claim-text> <claim-text>15. A method according to Claim 13 or 14 wherein the speed of the power takeoff output shaft is controlled by varying the auxiliary motor speed whilst the engine speed remains substantially constant.</claim-text> <claim-text>16. A method according to any one of Claims 13 to 15, wherein the power takeoff output shaft is deactivated by decoupling the first epicyclic gear element so that it can turn freely.</claim-text> <claim-text>17. A method according to Claim 16, wherein the auxiliary motor speed is reduced to reduce the speed of the power takeoff output shaft.</claim-text> <claim-text>18. A method according to Claim 17, wherein the first epicyclic gear element is coupled to the brake when the power takeoff output shaft speed falls below a predetermined value.</claim-text> <claim-text>19. A method according to any one of Claims 13 to 18, wherein the power takeoff output shaft is driven in reverse by coupling the first epicyclic gear element to the brake and operating the auxiliary motor in reverse.</claim-text> <claim-text>20. An agricultural tractor comprising a power takeoff drive system according to any one of Claims ito 12.</claim-text>