The present invention relates to a vehicle axle assembly having means for facilitating measuring of relative movement in the components thereof and especially, although not exclusively, a rear axle of an agricultural vehicle such as a tractor.

Increasingly, to improve efficiency in operation, modern agricultural vehicles such as farm tractors include computerised control systems linked to performance sensors distributed across the vehicle. For example, to improve efficiency and reduce damage to the ground during operation, modern tractors may be equipped with tyre pressure control systems or efficiency control systems as described in applicant's United States patents US9,078,391 and US9,095,089. In operation, these systems require a precise knowledge of the wheel load of each wheel or axle to enable, for example, the adjustment of tyre pressures without exceeding the tyre capability, or the generation of an optimised load distribution profile to provide guidance to the operator on ballasting of the tractor.

It is well known, for suspended axles, to determine the wheel load by measuring the pressure in the hydraulic or pneumatic cylinders of the suspension. However, in the case of a tractor, only the front axle is equipped with such a suspension system from which the wheel load may be determined, so the rear axle requires a different solution. According to one approach, it is known to use axle bearings which are equipped with load sensing means. These means require changes in the axle installation and are costly. Furthermore, optional usage is not generally an economic option due to the impact of the changes on the complete axle design and the resulting costs.

United States patent US 4,173,259 describes a load sensing device which senses deformation of the rear drive housing of a tractor to control the draft load by raising or lowering of an implement. The sensing may be electrical or mechanical and the signal produced by the strain on the rear drive is amplified and used to control a hydraulic control valve to a hydraulic weight distribution system. None of the above systems, however, address directly the issue of active or predictive monitoring of the mechanical components of an axle assembly to identify when a fault condition may occur.

It is, therefore, an object of the invention to provide an improved axle assembly which mitigates at least some of the above problems and which may additionally be used in the determination of vehicle axle loading.

In accordance with a first aspect of the present invention there is provided a vehicle axle assembly comprising an axle shaft in the form of an elongate body extending along an axis of rotation, and an axle housing partially surrounding and rotatably supporting the axle shaft, wherein a first planar portion extends from the axle shaft perpendicular to the axis of rotation and a second planar portion extends from the axle housing adjacent and substantially parallel to the first planar portion, and at least one sensor arrangement having a first sensor part on the first planar portion and a second sensor part on the second planar portion, with the at least one sensor arrangement being configured to generate a signal indicative of a measured gap between the first and second planar portions. The signal indicative of a measured gap need not indicate an absolute value for the gap width, but may instead comprise e.g. a measure of signal strength to a sensor on the wheel performing a different function such as transmitting data from an on-wheel tyre pressure sensor.

Preferably, the vehicle axle assembly further comprises a data processor coupled with the at least one sensor arrangement and with data storage holding a value representative of an expected gap between the first and second planar portions, the data processor being arranged to generate an alert if the measured gap and expected gap differ by more than a predetermined extent. The data processor and/or data storage may be stand-alone devices or may be part of a vehicle management system of a vehicle including the axle assembly. The alert generation indicates to a user that the gap has changed which may be representative of serious problems such as wear of the axle assembly or bearings within the housing, such as to allow the axle shaft to move inwards or outwards relative to the housing. An axle assembly including such a monitoring means as described in the preceding paragraph suitably further comprises one or more temperature sensors coupled with the data processor, with the data processor being arranged to adjust the expected gap value by reference to a sensed temperature. As will be understood, variations in ambient temperature together with differing thermal expansion characteristics for the materials of axle shaft and housing may cause gap variations which are not due to component wear and which should not be signalled as alarm conditions.

The value representative of an expected gap may be one that is loaded to data storage as a factory setting, or may be loaded to data storage by the data processor from a previously measured gap, optionally with storage of a history of gap measurements or representative values to support predictive maintenance scheduling.

Preferably two or more sensor arrangements are utilised, with each having a first sensor part on the first planar portion and a second sensor part on the second planar portion. Suitably, the sensor parts of the two or more sensor arrangements are regularly spaced on a predetermined radius about the axis of rotation of the axle shaft. With multiple sensors disposed around the axle, bending of the axle (and hence axle loading inducing the bending) may be determined as will be described hereinafter.

Preferably the sensor arrangement(s) are in form of discs (stator, rotor) aligned on the axis of rotation and which can provide signals from the whole circumference thereof.

The present invention further comprises a vehicle, and preferably a farm tractor, including such an axle assembly.

The present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a representation of a tractor; and

Figure 2 shows a section through a part of a rear axle assembly with additional components represented schematically. Referring to Figure 1, a tractor 10 is shown having a cab 12 and an engine compartment 14. A chassis 16 which is partly visible connects front wheel mounting 18 and rear axle assembly 20. The front wheel mounting 18 is equipped with an independent wheel suspension as described in applicants granted patent EP 1 627 762 with upper and lower transverse links mounting steered wheel hubs to the chassis and with vertical movement of each hub being damped by a respective hydraulic cylinder. As mentioned previously, the load of the front axle can be determined by measuring the pressure in the hydraulic cylinders of the suspension.

Figure 2 shows a sectional view through a part of the rear axle assembly 20 which includes an axle shaft 22 in the form of an elongate body extending along an axis of rotation R. The shaft 22 has an end flange 24 in the form of a first planar portion extending from the shaft perpendicular to the axis of rotation: the flange 24 provides the attachment point for a wheel carried by the axle.

An axle housing 26 partially surrounds the axle shaft 22, expanding to a trumpet housing (to the right of the figure) which in turn is connected to a centre differential (not shown) of the rear axle assembly. The axle housing 26 rotatably supports the axle shaft 22 by means of taper roller bearings 28, 30. From the housing 26, a second flange or planar portion 32 extends outwardly from the housing to lie adjacent and substantially parallel to the first planar portion 24.

A first sensor arrangement 34 has a first sensor part 34a on (or preferably inset into) the first planar portion 24 and a second sensor part 34b on (inset into) the second planar portion 32. The sensor parts 34a, 34b are the same radial distance from the axis of rotation R such that they pass in close proximity once in each revolution of the axle shaft 22. Different types of sensor arrangement may be used, such as a permanent magnet for the first part 34a and induction loop for the second part 34b, with the sensor arrangement being configured to generate a signal indicative of a measured gap G between the first and second planar portions 24, 32 when the sensor parts are aligned.

A data processor 36 is coupled with the sensor arrangement 34 and with data storage 38. The processor 36 and store 38 may be stand-alone units, or may comprise functions of a general engine management system for the tractor 10. In one embodiment, the store 38 holds a value representative of an expected gap between the first 24 and second 32 planar portions, with the data processor 36 being arranged to generate an alert if the measured gap G and expected gap E differ by more than a predetermined extent.

The expected gap E may be a factory set value, in which case an initially generated alert on start-up may be indicative of incorrect fitting of the axle shaft 22 or bearings 28, 30 or subsequently may be indicative of wear of these components. As an alternative, the expected gap E value may be captured as a measured gap G value and subsequently held in store 38.

As indicated generally at 40, further sensor arrangements are suitably provided spaced around the axis of rotation R to enable the capture of multiple measurements Gi , G ₂ etc. for the gap between the first 24 and second 32 planar portions. With multiple measurements and comparison between them or with stored expected value(s), the processor 36 determines from the variations an angle between the normally parallel (in unloaded conditions) first 24 and second 32 planar portions. This angle is a result of axle shaft 22 bending as axle load increases. Data store 38 holds a look-up table 42 from which the data processor 36 obtains a value for axle loading based on the extent of axle shaft bending as represented by the angle between the first 24 and second 32 planar portions. Instead of a look-up table, the data processor 36 may apply a predetermined linear function to derive the loading based on the axle shaft bending.

In the foregoing the applicants have described a vehicle axle assembly including an axle shaft 22 extending along an axis of rotation R, and an axle housing 26 partially surrounding and rotatably supporting the axle shaft. A first planar portion or flange 24 extends radially from the axle shaft 22 perpendicular to the axis of rotation, and a second planar portion or flange 32 extends radially from the axle housing 26 adjacent and substantially parallel to the first planar portion or flange 24. A sensor

arrangement 34 has a first sensor part 34a on the first planar portion 24 and a second sensor part 34b on the second planar portion 32, to generate a signal indicative of a gap between the first and second planar portions and indicate wear issues in the event of variations. From reading of the present disclosure, other modifications will be apparent to those skilled in the art. Such modifications may involve other features which are already known in the field of vehicle axles and component parts therefore and which may be used instead of or in addition to features described herein.