WO2011108948A1

WO2011108948A1 - Propulsion device and method

Info

Publication number: WO2011108948A1
Application number: PCT/NZ2011/000032
Authority: WO
Inventors: Robert Malcolm Sharp
Original assignee: Robert Malcolm Sharp
Priority date: 2010-03-05
Filing date: 2011-03-04
Publication date: 2011-09-09

Abstract

A propulsion system for a towed vehicle including: a rotatable traction element attached to the towed vehicle and configured to facilitate movement of the towed vehicle; a drive mechanism configured to rotate the traction element; and a sensor configured to sense a condition of the towed vehicle and to provide an output in response to the sensed condition, characterised in that the propulsion system includes a controller configured to receive the output from the sensor and to control the power delivered to the drive mechanism in response to the output.

Description

PROPULSION DEVICE AND METHOD

STATEMENT OF CORRESPONDING APPLICATIONS

This application is based on the Provisional specification filed in relation to New Zealand Patent Application Number 583731 , the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The invention relates to a method and device for propulsion of a vehicle, and in particular to a towed vehicle.

BACKGROUND ART It is well known that when a vehicle tows another vehicle, such as a loaded trailer, farm implement or articulated trailer etc, the towed vehicle places a considerable load on the towing vehicle. It generally does not take much of an increase in towing load before some modification of the towing vehicle is required. For example, vehicles specifically used for towing will generally have increased engine power, heavier duty transmission and improved braking systems in relation to vehicles not so designed. Furthermore, as traction is an important consideration, special tyres may be required for the towing vehicle. All of these can add significantly to the costs of a vehicle designed for towing when compared with a standard vehicle.

These problems can be highlighted in the example of farm vehicles where it is very common to use a tractor coupled to a towed implement, for example in preparing ground for planting or when harvesting a crop. In recent years, in a drive for greater efficiency, larger implements have been developed so that a greater area of ground / crop can be processed in a single pass by the tractor and implement. This has lead to the development of bigger, more powerful tractors to tow the larger implements. However this in itself can create new problems. For example, while larger tractors and implements may be fine on relatively flat open pasture land, the same may not be true on uneven ground where traction can quickly become a major concern.

Generally speaking, the larger the tractor (and towed implement) the more likely it is to slip, especially when moving up (or down) an incline. This can limit the usefulness of large tractors on sloping ground or may require special techniques to get a large tractor to the top of an incline, as discussed in more detail below. In either instance any benefit of using a larger tractor may be negated when used on sloping ground. It is common in New Zealand, and many other countries, for a farm to be fenced off into paddocks, in which case the useful size of a tractor may be limited by the existing gateways on a farm. For example, a typical gateway in New Zealand is around 3.6 metres (12 foot).

Therefore a farmer is limited to using a tractor that will pass through a 3.6 metre gateway or be faced with replacing all gateways which would be very expensive.

Another problem with the use of larger tractors is that their increased weight can lead to greater compaction of the soil. This is counterproductive in many instances, for example during preparation of the ground for seeding where the towed implement is being used to open up the ground. The more the ground is compacted the greater effort is required to move the implement through the soil, thus increasing the drag on the tractor, requiring further increase in power and so on.

Traction is a major problem in all towing situations. Generally, the wheels of the towing vehicle must provide sufficient traction to move the towing vehicle and to cope with the drag of the towed vehicle. While this can be a problem on any surface, it is particularly problematical when towing on unsealed surfaces and especially on a loose surface as is a common situation on a farm.

Generally speaking, as a vehicle gets larger and heavier, problems with traction will increase. These problems are exacerbated when towing an implement, such as a plough or seed drill, that places a significant load on the towing vehicle as the implement is pulled through the ground. In many towing situations, such as with a tractor and towed implement, the tractor can be operating close to the limit before traction is lost. Under these circumstances there is little margin for any variation in the conditions of operation before slipping can occur.

For example, an increase in slope, or a change in soil condition, can lead to loss of traction and slippage. Typically when this happens the wheels of the towing vehicle can spin, resulting in a lot of loose soil being thrown out behind the vehicle. This can form a wall or barrier in front of the towed implement (especially in the common situation on farms where the implement includes a roller), which can further increase the load on the towed vehicle due the increase drag created by the towed implement. This in turn can lead to a further loss of traction, thus exacerbating the problem. It is not uncommon on a farm to encounter an area of land in which the incline is too great for a tractor and implement to work up the incline. As a result when ploughing, seeding or otherwise operating a tractor and implement on the incline, the tractor and implement can only operate when moving downhill. This can lead to situations where the tractor and implement make one pass down the incline and then need to follow a track around the rise (following a path where the incline is such that the tractor and implement can move up it) until they return back to the top of the rise before making a further pass adjacent to the previous one down the incline. This situation can significantly increase the amount of time required to process the ground on the incline, as well as increased costs in operating the tractor and implement for the increased time for each circuit.

It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice. All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.

Throughout this specification, the word "comprise", or variations thereof such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.

DISCLOSURE OF THE INVENTION

According to one aspect of the present invention there is provided a propulsion system for a towed vehicle including:

a rotatable traction element attached to the towed vehicle and configured to facilitate movement of the towed vehicle; a drive mechanism configured to rotate the traction element ; and a sensor configured to sense a condition of the towed vehicle and to provide an output in response to the sensed condition, characterised in that.

the propulsion system includes a controller configured to receive the output from the sensor and to control the power delivered to the drive mechanism in response to the output. According to another aspect of the present invention there is provided a propulsion system for a towed vehicle, the system including:

a towing vehicle including a first coupling mechanism; a towed vehicle including a second coupling mechanism configured to engage with the first coupling mechanism on the towing vehicle, the towed vehicle having at least one rotatable traction element a drive mechanism configured to rotate the traction element a sensor configured to sense a condition of the towed and/or towing vehicles and to provide an output in response to the sensed condition

characterised in that the propulsion system includes a controller configured to receive the output from the sensor and to control the power delivered to the drive mechanism in response to the output. According to another aspect of the present invention there is provided a method of propelling a towed vehicle while it is being towed by a towing vehicle, characterised by the steps of:

a) sensing a condition of the towed vehicle with a sensor to provide sensed information; b) receiving the sensed information at a controller configured to process the sensed

information to provide processed information; and c) supplying power from the towing vehicle to a drive mechanism on the towed vehicle, the drive mechanism configured to rotate a traction element on the towed vehicle, where the amount of power supplied to the drive mechanism is determined by the controller in response to the processed information.

According to another aspect of the invention there is provided a method of propelling a towed vehicle substantially as described above, including the steps of: d) selecting an operational setting and communicating same to the controller; and e) using the controller to modify the power supplied to the drive mechanism in accord with the operational setting.

In one embodiment of the present invention a motor on a trailer is configured to drive at least one wheel of the trailer where the power for the motor is provided by a towing vehicle, such as a tractor. The amount of power provided to the motor on the trailer is controlled by a controller, which may be on the trailer or the tractor. A sensor is mounted on the coupling between the trailer and the tractor, the sensor providing output on the amount of force exerted by the tractor on the trailer (or vice versa) during towing. The controller may be programmed (or manually controlled) to alter the power provided to the motor on the trailer in response to the sensed force. The power delivered to the motor on the trailer may be altered to:

• reduce the drag of the trailer on the tractor; • increase the drag (act as a brake on the trailer); or

• increase the driving force so that the trailer pushes the tractor.

Reference to a towed vehicle throughout this specification should be understood to refer to a vehicle intended, in operation, to connect to the rear of another vehicle (to be referred to as the towing vehicle) such that the two vehicles move in unison, with steerage provided by the towing vehicle. The towing vehicle also includes a motor for propulsion of the towing vehicle.

In a preferred embodiment the towed vehicle is a farm implement.

There are numerous examples of farm implements in common use where the towed implement is typically configured to be towed by a tractor. Such implements include (without limitation) various forms of plough, seed drill and harvester. A common feature of most farm implements is that they are designed for operation on unsealed ground.

In a preferred embodiment the farm implement is a seed drill.

A seed drill is a common type of farm implement used to insert seed into prepared ground. Some preferred types of seed drill are configured such that a furrow is first opened in the ground, for example by use of a corrugated roller. A tube (typically a row of tubes, one for each furrow) follows in the opened furrows created by the corrugated roller, the tube used to insert a seed into the bottom of the furrow. A second roller may follow the tube, the second roller configured to close the furrow over the seed.

In other embodiments the towed vehicle may be any of the wide variety of vehicles that are normally towed, such as a trailer or caravan for example.

Reference to a rotatable traction element throughout this specification should be understood to refer to a wheel, roller or other circular device, typically arranged to revolve on an axle and used to facilitate the motion of a vehicle to which it is attached.

In a preferred embodiment the traction element is a wheel.

A wheel is commonly used on a towed vehicle to enable the vehicle to be moved over ground. However those skilled in the art will appreciate that other types of traction element, including a roller, may be used and reference throughout this specification to a traction element in the form a wheel only should not be seen as limiting.

In general a traction element may include features to improve traction of the element under normal operating conditions of use. For example a wheel may include a tyre where the tread of the tyre is configured to improve traction with soil. In some other embodiments a roller may be configured with grooves or protrusions (spikes etc) to improve traction of the roller as it moves over ground. The propulsion system of the present invention includes a drive mechanism configured to rotate the traction element. It is envisaged that the drive mechanism may be any form of drive as is well known in the art where the drive is used to turn a traction element such as a wheel. In one simple form this may be a chain drive (or belt drive) similar to that used for example to drive a wheel on a bicycle.

In other embodiments the drive mechanism may include a motor, for example an internal combustion petrol or diesel powered engine or an electric powered motor.

In a preferred embodiment a towing vehicle provides power for the drive mechanism.

In a preferred embodiment the power for the drive mechanism is provided through the power take off of a tractor.

In a preferred embodiment the drive mechanism includes an hydraulic motor.

An advantage of using a drive mechanism including an hydraulic motor is that it is common for many towing vehicles, such as tractors, to include a hydraulic system which can be coupled to attachments or implements through connection to a power take off (PTO) on the tractor. In such cases an hydraulic motor can be mounted on the towed vehicle with the hydraulic pressure provided by the hydraulic system of the towing vehicle.

A further advantage of this arrangement is that the weight of the propulsion system carried by the towed vehicle may be reduced as the main components of the hydraulic system (pumps, control valves, filters, reservoir and so on) are carried by the towing vehicle. In a preferred embodiment the drive mechanism is an hydraulic radial piston motor.

Use of an hydraulic radial piston motor may provide an efficient, long lasting, low maintenance drive mechanism which can provide high torque at relatively low speeds (ie. the relatively slow speeds normally used in operation of farm implements).

An hydraulic motor may be connected directly to a fixed axle connected to a pair of wheels for example. Operation of the motor would then provide a direct drive to the wheel. In some alternate embodiments a separate hydraulic motor may be used to power each wheel. In some arrangements a gear box may be used to transfer the power from the hydraulic motor to the wheels.

Alternate forms of motor, such as petrol, diesel or electric motors, may be used to power the wheel. However, each of these types of motor requires a separate fuel source which may add weight to the towed vehicle as well as requiring space for storage. An hydraulic motor may also require less maintenance and require less space than other forms of motor. An hydraulic motor may also be ideally suited to the production of high torque at low resolutions, as may be required to provide traction to the wheels during normal operation. In a preferred embodiment the condition of the towed and/or towing vehicle sensed by the sensor is a measure of a force exerted by the towed vehicle on a towing vehicle connected to the towed vehicle by a coupling and vice versa.

In a preferred embodiment the sensor is an electronic load sensor. In a preferred embodiment the sensor is mounted on a coupling between the towed vehicle and the towing vehicle.

Towed vehicles are typically connected to a towing vehicle by a coupling, which may be between a draw bar on a towing vehicle and a draw bar on a towed vehicle, for example.

Those skilled in the art will know that there are many methods of coupling a towed vehicle to a towing vehicle, and that reference to a draw bar on the towing vehicle and draw bar on the towed vehicle arrangement only throughout this specification should not be seen as limiting.

In a preferred embodiment the sensor is mounted on a draw bar of the towing vehicle.

A strain gauge may be used to detect the force applied at the coupling. Those skilled in the art will appreciate that various forms of strain gauge may be used. An advantage of mounting an electronic load sensor on the draw bar of the towing vehicle may be that the same sensor may be used when towing a variety of different vehicles. This may save cost, as only one sensor is used rather than one on each towed vehicle, as well as being generally convenient.

In all instances there will be a force exerted between the towing vehicle and the towed vehicle when the combination is in motion. This force, which is exerted at the coupling between the two vehicles, is commonly referred to as the drag of the towed vehicle on the towing vehicle. The drag, which may vary with speed and acceleration, is related to the amount of work that has to be provided by the motor of the towing vehicle in order to move the towing and towed vehicles along. The act of towing results in the drag force being exerted at the coupling between the two vehicles and may be measured, for example as a pressure exerted by the towing vehicle on the coupling.

In other embodiments the sensor is an hydraulic cylinder.

An hydraulic cylinder is a relatively simple way of detecting relative movement of two bodies, one connected to the body of the cylinder and one connected to a piston in the cylinder. As the bodies move relative to one another the piston is moved correspondingly and a change of pressure produced. A hydraulic cylinder may be attached to the coupling so as to measure the movement at the coupling when pressure is applied (or removed) during towing.

An advantage of using an hydraulic cylinder as the sensor is that the cylinder can be included in a hydraulic circuit configured to provide feedback to the master cylinder of the tractors hydraulic system. This may provide a direct feedback to control the output of the tractor's hydraulic system to the drive mechanism on the towed vehicle.

In a preferred embodiment the propulsion system includes an inclination sensor.

An inclination sensor is preferably mounted on the towing vehicle. Mounting an inclination sensor on the towing vehicle may provide similar advantages to those described above in relation to mounting the load sensor on the towing vehicle. Another advantage of an inclination sensor is that it may detect a change of slope of the ground over which the towing vehicle is moving. Information from the inclination sensor may be used to give an early warning that more power is required to drive (or brake) the towing vehicle and appropriate adjustments made.

Those skilled in the art will also appreciate that other indicators of the condition of the towed and/or the towing vehicle may be sensed, such as for example the detection of loss of traction by a wheel of the towing (or towed) vehicle, and that reference above to a sensor as a strain gauge or a hydraulic cylinder or, configured to sense a force at the coupling between the vehicles, should not be seen as limiting.

The drag force may be sensed relatively easily when the towing vehicle and towed vehicle are aligned, for example when the towing vehicle is moving in a straight line. However, when the towing vehicle turns the force on the coupling may change and allowance may need to be made for this in applying power to the drive mechanism of the towed vehicle. This may be necessary, for example, in embodiments where two wheels, one on either side of the towed vehicle, are driven by separate drive mechanisms. When the towed vehicle is not turning then the same power will generally be applied to each of the drive mechanisms. However, when the towed vehicle is turning, the wheel on the inside of the turn will revolve more slowly than the outside wheel. Hence less power is required for the drive mechanism of the inner wheel than for the drive mechanism of the outer wheel.

In a preferred embodiment the propulsion system includes an orientation sensor configured to determine the relative orientation of the towing vehicle to the towed vehicle.

An orientation sensor, configured to sense a change in direction of travel of the towing vehicle and/or towed vehicle, may provide information to the controller on the relative orientation of the two vehicles. The controller may be programmed (or otherwise configured) to adjust the power provided to the one or more drive mechanisms on the towed vehicle to compensate for/make allowance for the turning motion.

For example, if each of two wheels located on opposite sides of the towed vehicle are independently mounted and each attached to a separate drive mechanism, then the controller may provide different levels of power to each of the drive mechanisms to accommodate the different speeds of the wheels during turning. In some embodiments a mechanical component may be included in the axle linking two wheels on opposite sides of a towed vehicle. For example, a limited slip differential may be included in an axle system where both wheels are mounted on the common axle system driven by a single drive mechanism. Another method of determining how much work is being done by the motor of the towing vehicle during towing is to measure the load on the motor. For an internal combustion engine, as commonly used to power a tractor, this may be done by measuring the vacuum. Generally, as the load increases and greater power is output by the engine, the vacuum within the manifold is reduced. In some embodiments the sensor may be a vacuum gauge.

A vacuum gauge may be used to sense the vacuum in the manifold as a measure of the power being output by the engine. The sensed vacuum information may be sent to a controller which is programmed to adjust the power delivered to the drive mechanism of the towed vehicle in response to the sensed vacuum information. The propulsion system includes a controller configured to receive information from the sensors and to control the power delivered to the drive mechanism on the towed vehicle in response to the sensed information.

A controller may be any device capable of transforming the sensed information received from the sensor(s) and processing that information into processed information used to control the amount of power provided by the towing vehicle to the drive mechanism on the towed vehicle.

In some other embodiments the controller may be (or be part of) a programmable device, such as (without limitation) a computer or Programmable Logic Controller (PLC). Many modern towing vehicles have a built in computer system and a controller may conveniently be the inbuilt computer system or some part of it. In towing vehicles without an in-built computer system, or where that cannot be accessed, a dedicated computing system may be installed as a controller. The controller may be located on the towing vehicle (preferably) or the towed vehicle, although in all instances it must be configured to communicate with the sensor(s) and with the power drive of the towing vehicle (ie the power drive that provides power to the drive mechanism on the towed vehicle). In a preferred embodiment the power delivered to the drive mechanism is determined by the controller in response to at least one of the sensor outputs and in response to an operational setting.

In a preferred embodiment in which the operational setting is normal towing, the power delivered to the drive mechanism is calculated by the controller such that the drive mechanism reduces the force exerted by the towed vehicle on the towing vehicle. In this (normal) mode of towing, the wheels of the towed vehicle (or rollers of the seed drill etc) are driven to reduce the drag created by the towed vehicle.

In a preferred embodiment the power supplied to the drive mechanism in the normal towing mode is calculated by the controller such that the drive mechanism reduces the force exerted by the towed vehicle on the towing vehicle substantially to zero.

Reducing the drag of the towed vehicle may extend the operational conditions of operation of the two vehicles by enabling the towing vehicle to maintain traction in situations where this would not be possible if the towing vehicle had to pull the full weight of the towed vehicle. For example, as is well known by those skilled in the art, a tractor without a towed implement may be able to move on its own in conditions where attachment of a towed implement would cause it to lose traction and thus not be able to work.

A tractor coupled to a seed drill (or other farm implement) equipped with a propulsion system according to the present invention, with the operational setting in normal mode, may be able to operate in conditions in which a conventional system (without the present invention) would lose traction. This may be a significant advantage in extending the operational conditions for the tractor and implement to include conditions where a tractor and implement without the present invention could not operate. Such conditions may include the state of the ground being loose or muddy, perhaps as a result of weather conditions or previous vehicle operations.

A tractor coupled to a seed drill (or other farm implement) equipped with a propulsion system according to the present invention may be used to advantage when cultivating loose or muddy ground where, in a conventional arrangement, there is insufficient traction for the tractor to operate the implement. This may save costs due to avoiding the need to wait until the ground has firmed sufficiently to provide the required traction. Being able to sow in difficult conditions may be advantageous in terms of ensuring that seeds are planted at the correct. The present invention may also allow cultivation to occur earlier than would otherwise be possible (e.g. earlier in a season, when normal cultivation cannot be undertaken due to weather or ground conditions). This may allow a farmer to get a crop to market before others and hence to gain a better price for their produce.

In another preferred embodiment, in which the operational setting is braking, the power delivered to the drive mechanism is calculated by the controller such that the drive mechanism opposes the force exerted by the towing vehicle on the towed vehicle.

In this mode the drive mechanism is powered to slow down the wheels of the towed vehicle, thus increasing the braking. This mode of operation may be an advantage when operating a tractor and seed drill down an incline, in which case replacing the conventional push of the seed drill on the tractor with a breaking force pulling it back, may reduce any tendency for the wheels of the tractor to slip. This may allow a tractor and seed drill equipped with the present invention to work on steeper slopes without losing traction, or at least may provide safer operating conditions in normal situations by improving the braking force of the combined vehicles.

In a preferred embodiment, in which the operational setting may be referred to as driving or pushing, the power delivered to the drive mechanism is calculated by the controller such that the drive mechanism causes the towing vehicle to push the towed vehicle.

In this driving mode the drive mechanism is powered to drive the wheels of the trailer to the extent that the trailer pushes the towing vehicle. This mode may be used to advantage when towing up an incline, or when the ground conditions limit traction of a conventional system.

For example, a tractor coupled to a seed drill (or other farm implement) equipped with a propulsion system according to the present invention with the operational setting in drive mode, may be able to move up an incline on which a conventional system (without the present invention) would lose traction. This may be a significant advantage in reducing the time required to cultivate contoured ground, by enabling the vehicles to move more directly up and down an incline rather than moving around in a loop to get back to the top of the incline, thus saving operational costs and time for completion of the job.

The present invention may provide many advantages over the prior art conventional towing arrangements, including:

• Time and hence cost saving due to enabling the towed and towing vehicles to operate in ground conditions and on sloped terrain where conventional towing arrangements can lose traction;

• Operational cost saving as the towing vehicle and towed vehicle may be operated under a wider range of conditions, and therefore more frequently than conventional arrangements;

• Increased safety for the operator of the towing vehicle as in general the effect of the towed vehicle on the behaviour and handling of the towing vehicle is reduced and may even be beneficial, for example during braking;

• Reduced capital costs for the towing vehicle as the reduced need to provide traction to pull (or brake) a towed vehicle may result in a smaller, lighter and less powerful towing machine being able to tow a towed vehicle with a propulsion system of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which:

Figure 1 shows a schematic illustration of a propulsion system according to one

embodiment of the present invention; and

Figure 2 shows a schematic illustration of a propulsion system according to another

embodiment of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

A propulsion system for a towed vehicle is generally indicated by arrow 1 in Figure 1. The towed vehicle is generally indicated by arrow 2 and is in the form of a seed drill. The seed drill 2 includes a rotatable traction element 3 in the form of a wheel. A drive mechanism 4, shown schematically as a rectangular box, is a hydraulic motor configure to drive the wheel 3. A towing vehicle, in the form of a tractor, is generally indicated by arrow 7. A sensor 5, in the form of an electronic load sensor, is attached to a first coupling mechanism in the form of a draw bar 8, attached to the towing vehicle 7.

The sensor 5 is configured to sense a condition of the towed vehicle, namely a measure of a force exerted by the seed drill 2 on the tractor 7 on the coupling between the draw bar 8 and the draw bar 9. Information from the sensor 5 is transferred by cable to a controller 6 in the cab of the tractor 7.

Another sensor, in the form of an inclination sensor 10, is mounted on the tractor 7. The output of the inclination sensor, after averaging to remove the effects of vibration of the tractor, is sent to the controller 6. An orientation sensor 14, mounted on the coupling between the draw bar 8 and the draw bar 9, is configured to sense any change in orientation between the tractor 7 and the seed drill 2 and to relay this sensed information to the controller 6.

Power to drive the hydraulic motor 4 is provided by the tractor 7 via the power take off (PTO) 11. An hydraulic pump 12 is connected to the PTO 11 and provides hydraulic pressure through pipes 13 to the hydraulic motor 4. The amount of power delivered to the hydraulic motor 4 is controlled by the controller 6 which uses the information provided by the various sensors (5, 10, 14) to determine how much power is delivered through the PTO and therefore to the hydraulic motor. A typical arrangement also includes a sensor (not shown) on the gear shift of the tractor, the sensor used to transmit information to the controller as to which gear is engaged.

The controller also receives an operational setting from a switch operated by the operator of the tractor. This switch can be switched between normal, zero, brake and drive positions. In the normal position the controller 6 calculates the amount of power to be delivered through the PTO 11 to the hydraulic motor 4 on the wheel 3, taking into account the information provided by the various sensors (5, 10 14) so as to reduce the drag force at the coupling between the tow bar 8 and the draw bar 9 of the seed drill 2. The degree to which the drag force is reduced may be adjusted by an operator in the tractor 7 between limits of no reduction to full reduction (zero position, as occurs when the wheels 3 are being driven by the hydraulic motor 4 such that there is no force exerted between the tractor 7 and the seed drill 2).

When the operational setting is set to "brake" the controller 6 adjusts the power delivered through the PTO 11 to the hydraulic motor 4 in such a way that the wheel 3 is driven at a slower speed than the speed of the tractor 7, so that the seed drill 2 actively brakes the tractor 7. When the operational setting switch is in the drive position, the controller 6, again using the information sent by the various sensors (5, 10, 14), adjusts the power delivered through the PTO 11 so that the hydraulic motor 4 attempts to turn the wheel 3 faster than the wheels of the tractor 7, effectively using the hydraulic motor 4 to push the tractor 7.

Another embodiment of a propulsion system for a towed vehicle is generally indicated by arrow 20 in the schematic representation shown in Figure 2. Figure 2 shows a view from beneath a towed vehicle in the form a trailer 21. The trailer includes a pair of wheels 22 and 23, on opposite sides of the trailer body 24.

A drive mechanism, in the form of an electric motor 24 is connected via an axle 25 to the wheel 23 on one side of the trailer body.

A further drive mechanism, in the form of an electric motor 26 is similarly connected via an axle 27 to the wheel 23 on the opposite side of the trailer body.

The trailer 21 is configured to be towed by a towing vehicle in the form of a car, generally indicted by arrow 28. The car 28 includes a first coupling mechanism in the form a tow bar 29. The tow bar 29 is configured to couple to a second coupling mechanism, in the form a draw bar 30 of the trailer 21.

A sensor system 31 , in the form of a strain gauge and including an orientation sensor, configured to measure the relative orientation of the car 28 and trailer 21 is mounted in the vicinity of the coupling between the tow bar 29 and the draw bar 30 and is generally indicated by arrow 31 in Figure 2. Information from the sensor 31 is received by the controller 33 which is part of the car's computer system. The controller 33, having processed the information from the sensor 31 and having regard to the operator controlled operational settings (normal, brake and drive) determines how much current to deliver to the electric motors (24, 26) through wires shown schematically as dashed lines 34, 35 and 36 (where wire 34 terminates in the vicinity of the tow bar 29 and wires 34 and 35 are attached to the arms of the draw bar 30 and connected to 34 by an electrical coupling (not shown)).

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof as defined in the appended claims.

Claims

WHAT I CLAIM IS:

1. A propulsion system for a towed vehicle including: a rotatable traction element attached to the towed vehicle and configured to facilitate movement of the towed vehicle; a drive mechanism configured to rotate the traction element; and a sensor configured to sense a condition of the towed vehicle and to provide an output in response to the sensed condition, characterised in that the propulsion system includes a controller configured to receive the output from the sensor and to control the power delivered to the drive mechanism in response to the output.

2. A propulsion system for a towed vehicle, the system including: a towing vehicle including a first coupling mechanism;

a towed vehicle including a second coupling mechanism configured to engage with the first coupling mechanism on the towing vehicle, the towed vehicle having at least one rotatable traction element; a drive mechanism configured to rotate the traction element; and a sensor configured to sense a condition of the towed and/or towing vehicles and to provide an output relating to the sensed condition, characterised in that the propulsion system includes a controller configured to receive the output from the sensor and to control the power delivered to the drive mechanism in response to the output.

3. A propulsion system as claimed in either one of claims 1 or 2 wherein the towed vehicle is a farm implement.

4 A propulsion system as claimed in claims 3 wherein the farm implement is a seed drill.

5. A propulsion system as claimed in any one of the preceding claims wherein the traction element is a wheel.

6. A propulsion system as claimed in any one of the preceding claims wherein the towing vehicle provides power for the drive mechanism.

7. A propulsion system as claimed in any one of the preceding claims wherein power to the drive mechanism is provided through the power take off of a tractor.

8. A propulsion system as claimed in any one of the preceding claims wherein the drive mechanism includes an hydraulic motor.

9. A propulsion system as claimed in claim 8 wherein the drive mechanism is an hydraulic radial piston motor.

10. A propulsion system as claimed in any one of the preceding claims wherein the sensor is mounted on a coupling between the towed vehicle and the towing vehicle.

11. A propulsion system as claimed in any one of the preceding claims wherein the condition of the towed and/or towing vehicle sensed by the sensor is a measure of a force exerted by the towed vehicle on a towing vehicle or vice versa.

12. A propulsion system as claimed in any one of the preceding claims wherein the sensor is a strain gauge.

13. A propulsion system as claimed in any one of the preceding claims wherein the sensor is an hydraulic cylinder.

14. A propulsion system as claimed in any one of the preceding claims

including an orientation sensor configured to determine the relative orientation of the towing vehicle to the towed vehicle.

15. A propulsion system as claimed in any one of the preceding claims

including an inclination sensor

16. A propulsion system as claimed in any one of the preceding claims wherein the controller includes a programmable device

17. A propulsion system as claimed in claim 15 wherein the programmable device is a computer.

18. A propulsion system as claimed in claim 16 wherein the programmable device is a Programmable Logic Controller (PLC).

19. A propulsion system as claimed in any one of the preceding claims

20. A method of propelling a towed vehicle while it is being towed by a towing vehicle, characterised by the steps of:

a) sensing a condition of the towed vehicle with a sensor to provide sensed information;

b) receiving the sensed information at a controller configured to

process the sensed information to provide processed information; and

c) supplying power from the towing vehicle to a drive mechanism on the towed vehicle, the drive mechanism configured to rotate a traction element on the towed vehicle, where the amount of power supplied to the drive mechanism is determined by the controller in response the processed information.

21. A method of propelling a towed vehicle as claimed in claim 19 including the steps of:

d) selecting an operational setting and communicating same to the controller; and

e) using the controller to modify the power supplied to the drive

mechanism in accord with the operational setting.

22. A method of propelling a towed vehicle as claimed in either claim 19 or claim 20 wherein the power delivered to the drive mechanism is determined by the controller in response to the sensor output and an operational setting.

23. A method of propelling a towed vehicle as claimed in claim 21 wherein in one operational setting the power delivered to the drive mechanism is calculated by the controller such that the drive mechanism reduces the force exerted by the towed vehicle on the towing vehicle (normal operational setting).

24. A method of propelling a towed vehicle as claimed in claim 21 wherein in one operational setting the power supplied to the drive mechanism is calculated by the controller such that the drive mechanism reduces the force exerted by the towed vehicle on the towing vehicle substantially to zero (zero operational setting).

25. A method of propelling a towed vehicle as claimed in claim 21 wherein in one operational setting the power delivered to the drive mechanism is calculated by the controller such that the drive mechanism opposes the force exerted by the towing vehicle on the towed vehicle (brake operational setting).

26. A method of propelling a towed vehicle as claimed in claim 21 wherein in one operational setting the power delivered to the drive mechanism is calculated by the controller such that the drive mechanism causes the towing vehicle to push the towed vehicle (drive operational setting).

27. A method of propelling a towed vehicle as claimed in either claim 19 or claim 20 wherein the condition of the towed and/or towing vehicle sensed by the sensor is a measure of a force exerted by the towed vehicle on a towing vehicle or vice versa.

28. A method of propelling a towed vehicle as claimed in either claim 19 or claim 20 wherein the condition of the towed and/or towing vehicle sensed by the sensor is a measure of the relative orientation of the towing vehicle to the towed vehicle.

29. A method of propelling a towed vehicle as claimed in either claim 19 or claim 20 wherein the condition of the towed and/or towing vehicle sensed by the sensor is a measure of the inclination of the towing vehicle.

30. A propulsion system for a towed vehicle substantially as herein described with reference to and as illustrated by the accompanying description and drawings.

31. A method of propelling a towed vehicle substantially as herein described with reference to and as illustrated by the accompanying description and drawings.