GB2297068A - Drive for the wheels of a trailer - Google Patents

Abstract

A drive system for an agricultural trailer, slurry tanker or similar which carry 4-10 tonnes and spread the load gradually utilises the PTO of the towing vehicle 2 to drive the wheels 44 of the trailer. The drive reaches a differential which incorporates a reduction train 26, 28. The differential either receives drive from a predifferential reduction stage such as a sprocket wheel train or provides drive to a gear reduction train such as an epicyclic hub gearbox 38. A clutch on one of the half shafts is operable from the towing vehicle to cancel the drive allowing corners to be turned safely.

Description

SPREADER DRIVE TECHNICAL FIELD This invention concerns agricultural trailers, slurry tankers and spreader trailers for fertiliser, particularly those in the 4-10 tonne range.

BACKGROUND ART These are usually towed by a large tractor or truck.

Tractor wheels are usually run empty in order to reduce soil compaction. This reduces traction and makes it necessary to additionally drive the trailer wheels through the tractor PTO.

Such an arrangement gives adequate traction for ordinary conditions but in practice the provision of such a drive presents problems, firstly the reduction of the field speed rpm down to ground speed of the trailer wheels. Conventionally this would be attempted in two gearbox stages with corresponding increase in torque. Such an increase requires increased strength and stiffness in the transmission parts.

Secondly the towing geometry of the tractor and spreader means that the tractor wheels describe an arc different from the following trailer. The wind up which occurs in the shafts and transmission sometimes snaps components and expensive repairs result.

Two gearboxes in series introduces problems of space, weight and cost and the trailer still needs a differential to drive the half shafts of the trailer axle. This invention addresses these problems.

SUMMARY OF THE INVENTION This invention provides a trailer having at least one pair of driven wheels and a drive for the wheels capable of being coupled to the PTO of the towing vehicle characterised by a differential reduction gear assembly drivable by the PTO in combination either with a pair of reduction gear boxes one for each wheel both drivable by the differential gear assembly or a pre differential reduction stage.

The pre differential reduction stage may be a chain and sprocket drive.

In the differential it is convenient to provide the reduction through the crown wheel and pinion. This stage offers a reduction of the order of 3.5:1-10.1. The crown wheel may be part of an epicyclic train giving reduction before the drive reaches the half shafts. The crown wheel may be a gear ring with internal teeth with which the planetary pinions mesh. The epicyclic output then drives the half shafts.

The reduction gear boxes may be epicyclic in hub boxes.

This type of box is compact and can be incorporated easily into the drive train without extra ground clearance.

Furthermore they are capable of transmitting the high torque delivered by the differential. These are available with ratios which suit the road\field speed of the trailer.

A further significant advantage is the provision in the differential of a drive isolator which disengages and reengages the drive to the differential to permit the trailer to turn a corner. The isolator may be a clutch or mechanical equivalent which does not rely on the meshing of pinions the reason being that even a small degree of wind up renders engagement and disengagement difficult in practice. The clutch may be controlled from the cab of the towing vehicle by cable, solenoid, electric motor or equivalent. As only sliding dogs are involved interruptions to the drive are easily made with minimum shock to the drive train.

BRIEF DESCRIPTION OF THE DRAWINGS One embodiment of the invention is now described with reference to the accompanying drawings in which Fig 1 is a diagrammatic side view of the trailer and rear of the towing vehicle; Fig 2 is a diagrammatic partly sectioned plan of the trailer drive.

Fig 3 is a part sectional view of the pre differential stage.

BEST MODE OF CARRYING OUT THE INVENTION Referring to the drawings the towing vehicle 2 has a hitch 4 and a rear PTO 6. The trailer 8 has a towbar 10 which extends for about 2m in front of the trailer body. The body has sloping sides and holds 4 tonnes of fertiliser. The body is made of welded steel panels as described in our copending application for Patent 243 837.

The Eaton Corporation of Cleveland Ohio supply among others an EATON (Registered Trade Mark) series 22 2-speed differential axle. The ratio choices are as follows: 3.90/5.32, 4.11/5.61, 4.33/5.91 ,4.62/6.31, 4.88/6.65, 5.29/7.21, 5.57/7.60, 6.17/8.41, 6.50/8.86, 7.17/9.77.

A single rigid axle 12 and differential casing 14 support the body on leaf springs 16. The PTO of the towing vehicle 6 is coupled to a drive shaft 18 which is directed rearwards through transverse beams 20 to the differential casing 14. Pinion 22 meshes with a 17 in crown wheel 24 giving a 3.2:1 reduction.

Planet pinions 26 mesh with the internal teeth of crown wheel 24. Pinions 26 also mesh with sun gear 28 which turns half shaft 30. The differential cluster 32 also turns half shaft 34. Each half shaft drives the sun wheel 36 of a epicyclic hub gearbox 36 (one shown). The planet wheels 40 drive the annulus 42 to which is bolted tyred wheel 44.

This stage gives a 3:1 reduction and increases torque without requiring shafts and other transmission parts to take extra force.

The drive from the PTO to the differential must be interrupted occasionally as spreading proceeds in order to prevent wind up. The differential has a selector 46 moved by a hydraulic ram 48. The original purpose was to shift between a high ratio and a low ratio thereby doubling the number of ratios available to the driver. The hydraulic lines 50 extend to the towing vehicle and a cab control (not shown).

The selector is adjusted to retain one of the DRIVE positions and to establish a NEUTRAL position between the two original drive positions. The selector 46 has a synchromesh function which allows the dogs to engage and disengage as in speed matching. The trailer wheel freewheels when one half shaft 30 is put in NEUTRAL.

It is usual to put the differential into NEUTRAL each time the spreader turns a corner.

The drive in Fig 2 utilises the differential epicyclic gears and the hub epicyclic gears to give the required reduction. In Fig 3 the hub gearboxes are substituted with standard hubs and the differential housing has an integral chaincase 54. A sprocket 56 receives drive from input shaft 18 and drives a chainwheel 58. The chainwheel drives the differential bevel pinion 22.

We have found the advantages of the above embodiment to be: 1 Simple accessible transmission layout.

2 Economical step down components.

3 Danger from wind up minimised.

4 Epicyclic boxes are able to transmit the torque resulting from the differential step down.

Claims (11)

Claims

1 A trailer having at least one pair of driven wheels and a drive for the wheels capable of being coupled to the PTO of a towing vehicle characterized by a differential reduction gear assembly drivable by the PTO in combination with either a pair of reduction gear boxes or a pre different:al reduction stage.

2 A trailer as claimed in claim 1 wherein the crown member of the differential is part of an epicyclic train.

3 A trailer as claimed in claim 2 wherein the crown member is gear ring with internal teeth and planetary pinions.

4 A trailer as claimed in claim 2 or 3 wherein a drive isolator disengages and reengages the differential to permit the trailer to drive around a curve.

5 A trailer as claimed in claim 4 where the isolator is a clutch.

6 A trailer as claimed in claim 4 or 5 where the isolator is operable from the towing vehicle.

7 A trailer as claimed in any one of claims 1-6 wherein the pre-differential stage is a chain and sprocket drive.

8 A trailer as claimed in any one of claims 1-6 wherein the reduction gearboxes are epicyclic.

9 A trailer as claimed in claim 8 wherein the reduction gearboxes are each a wheel hub reduction box.

10 A trailer as claimed in claim 8 wherein the ratios are 1: about (1.5 - 3).

11 A trailer substantially as herein described with reference to and as illustrated in Figs 1 and 3 or as modified by Fig 3 of the accompanying drawings.