POWER TRANSMISSION COUPLING

Abstract: A power transmission coupling for driving the wheels (1) of a trailer from a power take off on a tractor unit towing the trailer unit. The coupling comprises a clutch (6) having an input for connection to the power take off (15), and an output (5) for connection to a power transmission input of the trailer unit. The tension in the coupling when it connects the tractor and trailer units is monitored, and the slippage of the clutch (6) is controlled in response to the monitored tension so as to maintain the speed at which the trailer unit is driven substantially the same as the speed at which the tractor unit is driven.

Description: POWER TRANSMISSION COUPLING The present invention relates to a power transmission coupling for driving the wheels of a trailer from a power take off ori a tractor unit towing the trailer unit. There are many circumstances in which it is desirable to be able to drive the wheels of a trailer being towed by a tractor unit. Driving the wheels of the trailer increases the combined traction of the tractor and trailer. This reduces the chances of the tractor and trailer becoming bogged down in soft ground and increase the ability of the tractor and trailer to travel up an incline in wet conditions for example. Particularly in the case of agricultural machinery the ability to drive the wheels of the trailer can dramatically improve the usefulness of a trailer unit by for example increasing the load which can be carried by the trailer or by increasing the range of uses to which the trailer unit can be put. Agricultural tractors are_ typically _provide with a power take off which is driven at a speed related to the tractor engine. Thus by coupling the power take off to the power transmission of a trailer the wheels of the trailer can be driven directly by the tractor. It is however highly desirable to ensure that the driven speed of the tractor wheels is substantially the same as the driven speed of the trailer wheels as if this is not the case wheel slip must inevitably occur. This can be achieved by matching trailer units to particular tractor units so that the wheel sizes of the trailer and tractor units and the gearing of the power output and the traileς transmission .are such as to avoid wheel slip when the tractor is driven in a particular gear along a linear path. Unfortunately it is often highly desirable to be able to drive the tractor in any of its gears but changing gear in the tractor results in a mis-match between the tractor wheel speed and the trailer wheel speed and therefore in the known tractor-to-trailer coupling units trailer drive can only be selected when the tractor is in a particular predetermined gear. Even when matched tractor and trailer units are available and the appropriate tractor gear is selected, when the tractor turns a corner the trailer will generally follow a path inside that followed by the tractor. The distance travelled by the trailer is thus less than that followed by the tractor and therefore the trailer "pushes" the tractor. This can cause jack-knifing with potentially serious consequences. Thus in practice few trailers used in general agricultural work have driven wheels. * It is an object of the present invention to obviate or mitigate the above problems. According to the present invention there is provided a power transmission coupling fa driving. the wheels of a trailer from a power take off on a tractor unit towing the trailer unit, the coupling comprising a clutch having an input for connection to the power take off, an output for connection to a power transmission input of the trailer unit, means for monitoring the tension in the coupling when it connects the tractor and trailer units, and means responsive to the monitored tension to control the slippage of the clutch so as to maintain the speed at which the trailer unit is driven substantially the same as the speed at which the tractor unit is driven. Preferably the clutch is designed so as to slip in all normal conditions, the speed of the input to the clutch being sufficiently high that if the input and output speeds of the clutch are the same the driven speed of the trailer is equal to or greater than the speed of the tractor in its highest gear. The tension in the coupling can be monitored by a spring loaded lever system which fully releases the clutch when the tension is zero but progressively reduces the slippage in the clutch as the tension increases from a predetermined level. Thus as the tractor unit pulls away the tension in the coupling increases, increasing the torque delivered to the clutch output as the clutch engages progressively. The trailer unit is then driven to follow the tractor unit. As the trailer unit effectively catches up with the tractor unit the tension in the coupling unit is reduced and the slippage in the clutch increases. There is thus effectively a feed back system which ensures that the slippage on the clutch is just sufficient to match the speed across the ground of the tractor and trailer units. Tne clutch may be in the form of a splined shaft which ro-tates with or_____ox_jnore clutch. pXaJtes. that are free to slide along the shaft. The splined shaft is received within a splined housing that rotates with at least one furthe ■ clutch plate, the further clutch plate being slidable relative to the housing. The slippage of the clutch is determined by controlling the pressure applied between mating faces of the plates. An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which : Fig. 1 illustrates a power transmission coupling in accordance with the invention; and Fig. 2 is an enlarged view of a detail of. Fig. 1. The drawings are highly schematic illustrations of a power transmission coupling intended to connect an agricultural tractor (not shown) to a trailer unit only the transmission shaft, back axle and wheels of which are shown. Referring to the drawings, the trailer comprises a pair of rear wheels 1 (only one of which is shown) driven from a differential 2 by a conventional transmission shaft 3. The forward end of the transmission shaft is connected by universal joint 4 to the end of an output shaft 5 of a clutch assembly 6, the output shaft running in sealed bearings 7. The output shaft 5 is fixedly secured to a splined body 8 on which a series of annular clutch plates 9 are axially slidable. The splined body 8 cannot move axially relative to the clutch assembly 6. A cup shaped housing 10 which is provided with axially extending internal splines is arrange around the oody 8 and is engaged internally be a series of annular clutch plates 11, the plates being slidable axially relative to the housing 10. Plates 11 are arranged alterna.tely. with the plates 9 .so that __?ach plate 11 is constrained to rotate with the housing 10 between a pair of plates 9 which are constrained to rotate with the body 8. The housing 10 is supported in sealed bearing 12 so as to be prevented from moving axially relative to the assembly 6. The housing 10 is driven by transmission shaft 13 connected by a conventional universal joint 14 to a splined power take off 15 of a tractor unit (not shown). The joint 14 can slide axially relative to the power take off 15. A clutch actuating member 16 is slidable axially relative to the transmission shaft 5 and can rotate relative to a bearing plate 17 secured by a rod 18 to a lever 19. The lever is pivotal about pivot point 20 and is pivotally connected by a rod 21 to a spring loaded actuator 22. One end of the actuator unit 22 is connected to the tractor unit (not shown) and the other end is connected to the rod 21. The actuator unit 22 is slidably supported on a frame member 23 which supports the clutch assembly 6. Thus the position of the actuator member 22 relative to the frame member 23 corresponds to the pulling force applied by the tractor unit to the trailer unit, and this pulling force corresponds to the tension in the coupling. The clutch assembly 6 incorporates an oil bath so that the clutch plates 9 and 11 run in the oil which serves both to provide a controlled degree of slip between the plates 9 and 11 and to dissipate heat generated by the friction between the plates 9 and 11. When the tractor unit sets off in the forward direction the clutch is initially disengaged but as the tension in the actuator unit 22 builds up it moves to the left in F_g._ 1..cela± ve to the. _ tame, member 23 and as a result the member 16 compresses the series of plates 9 and 11 together, the pressure determining the torque transmitted to the output shaft 5. The trailer wheels 1 are thus driven and the trailer begins to follow the tractor unit. The speed at which the trailer moves increases until the tension in the actuator 22 decreases, thereby reducing the pressure on the plates 9 and 11 and reducing the torque delivered to the output shaft 5. The slippage within the clutch is thus adjusted to be sufficient to match the speed of the trailer unit to that of the tractor unit. It would be possible, to associate with the actuator 22 a device which automatically applies brakes provided on the trailer unit if the trailer unit starts to push the tractor unit, as could occur for example if the tractor unit is attempting to move slowly down a steep incline with the trailer unit behind it. Such an arrangement is not shown in the accompanying drawings. The illustrated arrangement can provide drive in only one (the forward) direction. It would however be possible to provide a separate clutch assembly operating in the reverse sense to that illustrated to enable the trailer wheels to be driven in reverse when the tractor unit is pushing rather than pulling the trailer unit. It would be possible for a tractor unit to become bogged down in soft ground and unable to move forward. In such a circumstance the tractor would not be able to apply tension to the coupling and therefore it would not be possible for drive to transmitted to the trailer wheels. To cover such an eventuality it would be possible to provide a mechanical, and/or hydraulic override system which, would enable the clutch mechanism to be engaged temporarily to enable the trailer unit to effectively push the tractor unit.

Claims: CLAIMS: 1. A power transmission coupling for driving the wheels of a trailer from a power take off on a tractor unit towing the trailer unit, the coupling comprising a clutch having an input for connection to the power take off, an output for connection to a power transmission input of the trailer unit, means for monitoring the tension in the coupling when it 10 connects the tractor and trailer units, and means responsive to the monitored tension to control the slippage of the clutch so as to maintain the speed at which the trailer unit is driven substantially the same as the speed at which the tractor unit is driven. -_ - 2. A power transmission coupling according to claim 1, wherein the clutch is designed so as to slip in all normal conditions. 3. A power transmission coupling according to claim 1 or 2, wherein the tension in the coupling is 2 0 " monitored by a spring loaded lever system which fully . eleases the ___Iut_ch when the tension is zero but progressively reduces the slippage in the clutch as the tension increases from a predetermined level. 4. A power transmission coupling according to 2 5 any preceding claim, wherein the clutch comprises a splined shaft which rotates with one or more clutch plates that are free to slide along the shaft, and a splined housing which rotates with at least one further clutch plate that is slidable relative to the 30 housing, the shaft mounted clutch plates being arranged adjacent the housing mounted clutch plates, and the slippage of the clutch being determined by controlling the pressure applied between the faces of the adjacent, plates. ' 5 5. A power transmission coupling according to any preceding claim, comprising manually actuable means for controlling the slippage of the clutch. 6. A power transmission coupling substantially as hereinbefore described with reference to the accompanying drawings.

Inventors: GARDNER JOSEPH, GARDNER, JOSEPH
Applicants: GARDNER JOSEPH, GARDNER, JOSEPH
Application year: 1986
Main classification: B62D59
IPC codes: B62D59