GB2484521A

GB2484521A - Tractor hitch control system

Info

Publication number: GB2484521A
Application number: GB1017373.0A
Authority: GB
Inventors: Jacques Pirotais
Original assignee: AGCO SA
Current assignee: AGCO SA
Priority date: 2010-10-14
Filing date: 2010-10-14
Publication date: 2012-04-18
Also published as: GB201017373D0

Abstract

A tractor hitch control system 100 comprises a linkage assembly 26 having a pair of lift arms 30 for attachment to an implement. A lift actuator, for example a hydraulic cylinder 34 controls the height of the lift arms. The system further comprises means to measure the downward force exerted on the lift arms. The front hitch is operable in a weight transfer mode in which said downward force is controlled. The actuator 34 maybe a double-acting hydraulic cylinder. The means to measure the downward force maybe a pressure sensor 70 which measures the pressure on one side of the hydraulic cylinder.

Description

DESCRIPTION

TRACTOR HITCH CONTROL SYSTEM

The invention relates to the control of hitches mounted to agricultural tractors and to which implements can be attached. In particular, the invention relates to linkage assemblies having a lift actuator for controlling the height of the lift arms.

Since the conception of agricultural tractors, economic pressures and the desire for larger machinery have driven the increase in power leading to tractors of ever-increasing size and weight. Whilst bigger tractors can handle larger implements and, thus, reduce the number of passes across a given field, the impact on the soil surface becomes more significant.

More recently, environmental pressures are placed upon farmers to reduce soil compaction so as to preserve the integrity of the underlying soil structure. The ground pressure exerted by tractors is dependent upon the weight and contact area with the ground. The continued desire for high horsepower machines limits the extent to which weight can be reduced, thus placing more focus on the increase of ground contact area.

Efforts to achieve this, especially for soil working, include the use of wider tyres, lower inflation pressures and increased number of wheels and/or even axles. Despite these efforts, the practical requirements of a multi-use tractor, maximum width for example, limit such methods.

There remains a significant desire to lower the ground pressure of conventional tractors. It is, therefore, an object of the invention to provide improvements to a tractor to assist in the lowering of ground pressure.

In accordance with the invention there is provided a tractor hitch control system comprising a linkage assembly having a pair of lift arms for attachment to an implement and a lift actuator for controlling the height of the lift arms, the system further comprising means to measure the downward force exerted on the lift arms, wherein the front hitch is operable in a weight transfer mode in which said downward force is controlled. By controlling the downward force exerted on the lift anus, weight can be transferred from the tractor to an implement in a controlled manner. A farmer may, therefore, transfer a portion of the tractor's weight onto a front packer for example which runs over land not impacted by the tractor, namely the strip between the tractor track. Advantageously, this increases tile ground contact area over which the tractor weight is distributed thus reducing ground compaction.

The invention is particularly beneficial when working on soil, for cultivation or drilling for example. Furthermore, due to the beneficial use on soil working involving hauled implements, the invention offers particular advantages when applied to front linkage assemblies. In particular, a front packer may be mounted to a front linkage whilst a seed drill is mounted to the rcar. The front packer serves to spread the weight and reduce thc inipact of the tractor tyres upon the soil. The invention alleviates the need for a heavy front packer traditionally employed to hide' the mts left by the tyres. Instead, a lighter front packer can be used wherein the weight of the tractor is exploited. Moreover, the reduced weight of the overall tractor/front packer combination reduces fuel consumption.

Preferably, the lift actuator is a double-acting hydraulic cylinder. It will, of course, be appreciated that the lift arms may comprise more than one lift actuator.

In an alternative embodiment, the lift actuator comprises an electric motor.

The means to measure the downward force is preferably a sensor which measures the pressure on one side of a piston in the hydraulic cylinder.

In a preferred embodiment a supply of pressurised fluid to the lift cylinder is controlled to maintain the downward force within a target range which may be set by a user via a driver terminal.

Further advantages of the invention will become apparent from the following description of a specific embodiment with reference to the appended drawings in which:-Figure 1 is a schematic side view of an agricultural tractor having a seed drill mounted to the rear and a packer mounted to the front; Figure 2 is a schematic view of a control system in accordance with the invention shown with a plurality of controllable operating components and sensed functions upon the tractor of Figure 1.

With reference to Figure 1, an agricultural tractor 10 comprises rear wheels 12 and steerable front wheels 14. The tractor 10 is of a known construction and will not be described in detail.

I

A seed drill 110 is shown mounted to the rear of the tractor by a drawbar 48 in a known fashion. Other hydraulic and/or electric connections may be included between the tractor 10 and seed drill 110 but are omitted for clarity.

A packer (or roll) 120 is shown mounted to the front of the tractor and will be described in more detail below.

With reference also to Figure 2 a control system 100 comprises an electronic control unit (ECU) 16 which includes a microprocessor operating in accordance with the invention. The various operating functions and components of the tractor connected to the ECU will now be described in turn. It should be appreciated however, that not all functions controlled by the ECU are relevant to the control of the front hitch but a description is included for completeness.

Engine management The tractor 10 comprises an internal combustion engine 18 (designated by a dashed box in Figure 1). An engine control unit 20 is connected to engine 18 and serves to sense a variety of real time operating parameters associated with the engine 18 and control a plurality of variables accordingly. It should be understood that engine control unit 20 may be integrated into ECU 16.

Sensors (not shown) measure the temperature of the engine 18, the engine speed and the engine load, each of which is considered a real time operating parameter for the purpose of this specification. The operating parameter values are preferably transmitted to the ECU 16 in real time.

Control signals are transmitted from the ECU 16 to the engine control unit 20 to control the speed of the engine 18.

Transmission Tractor 10 comprises a transmission 22 of known construction and which serves primarily to deliver power (or torque) from engine 18 to the wheels 12,14 with a variable input-to-output speed ratio. Sensors (not shown) embedded in transmission 22 serve to sense the real time transmission ratio the resultant signals from which are transmitted to ECU 16. Control signals are transmitted in exchange from ECU 16 to transmission 22 to control the input-to-output ratio. It will be appreciated that transmission 22 may include ratio changing apparatus of known construction which may include clutches, hydraulic actuators and/or hydraulic pumps and motors. Furthermore the transmission may be of various constructions and types, the specific format not being critical to the invention. For example, the transmission may be of a stepped or stepless ratio type.

Together the engine 18 and transmission 22 dictate the ground speed and acceleration of the tractor.

Power take off (PTO,,) A rear PTO stub 58 is driven via a rear PTO clutch 60 which is controlled by control signals transmitted from ECU 16. Also a rear PTO sensor 62 measures the rotational speed of rear PTO stub 58 and transmits a corresponding signal in the form of a real time operating parameter to ECU 16.

Similarly, a front PTO system may be included but is omitted for clarity.

Rear Hitch and Drawbar As in known tractor set-ups, tractor 10 comprises a rear hitch 28 for the attachment of implements. The rear hitch 28 comprises a pair of lower links 32 which form part of a known three-point linkage system. Lower links 32 are lifted and lowered by hydraulic cylinder 36.

The height of the linkage 28 is sensed by a sensor 42 which measures the position of piston 36a in the cylinder 36. The sensor readings representative of rear hitch position are transmitted to the ECU 16.

The rear hitch 28 has associated therewith a hydraulic control unit 46 which is hydraulically connected to the lift cylinder 36 for the purpose of controlling lifting and lowering thereof Electrical control signals are transmitted froni ECU 16 to the hydraulic control unit 46 to control the height of the rear hitch 28.

The rear hitch 28 can be controlled in accordance with a plurality of different modes, as per tractors today. For example, the absolute height of the hitch may be set. Alternatively, the hitch may operate in a temporary or steady sink' mode in which the hitch is allowed to lower to its minimum height depending upon the behaviour of the aftached implement and/or ground contour.

Furthermore, the tractor comprises a drawbar 48 extending from the rear thereof and which is provided to tow implements. The hitch draft is measured by sensor 50 associated with a drawbar support mechanism. The measured hitch draft is transmitted by sensor 50 to ECU 16 in the form of a real time operating parameter.

Front Hitch and Control System The tractor 10 also comprises a front hitch 26 which is similar in principal to the rear hitch 28 described above. The front hitch comprises a pair of lower links 30 which arc pivotally mounted relative to the tractor chassis. Together with a top link 31, the lower links 30 form a three-point linkage. As with the rear hitch, lower links 3o are lifted and lowered by a hydraulic cylinder 34 connected between the tractor chassis and the lower links 30. Although only one cylinder 34 is shown, it should be appreciated that the assembly may comprise a pair of cylinders of similar construction.

The height of the front linkage 26 is sensed by a sensor 40 in a similar manner to the rear linkage. The sensor readings representative of rear hitch position are transmitted to the ECU 16.

The front hitch 26 has associated therewith a hydraulic control unit 44 which is hydraulically connected to the lift cylinder 34 for the purpose of controlling lifting and lowering thereof Electrical control signals are transmifted from ECU 16 to the hydraulic control unit 44 to control the height of the lower link arms 30. Pressurised fluid is supplied and received from the chambers 34a, 34b located either side of a piston 34c. Cylinder 34 is double acting and can exert a downward force on the lift arms.

A pressure sensor 70 is hydraulically connected to the first chamber 34a of cylinder 34 and measures the hydraulic pressure therein. The sensed pressure is comnmrnicated electrically to the ECU 16.

Driver Terminal A user interface device in the form of a terminal 80 includes a display 82, a plurality of sliding buttons 84, and a scrolling wheel 86. In this example the display 82 is touch sensitive although a conventional display may be used without deviating from the invention. Likewise the manual buttons 84 may be replaced with aheniative fonns or excluded.

The terminal 80, typically mounted to the right-hand side of a driver in the cab, is in wired or wireless communication with ECU 16. Commands from the driver, and inputted via the terminal 80, are transmitted to ECU 16. Display 82 is driven by signals transmitted from ECU 16. The display 82 may, for example, display various real time operating parameters associated with various operating functions of the tractor.

The terminal 80 includes means to receive a data storage device such as an SC card 88.

Weight transfer mode The tractor 10 is capable of operating in a weight transfer mode in which a downward force is applied to the lower links 30 of the front hitch 26 thereby transferring a controllable portion of the tractor weight onto the front-mounted press 120.

In the weight transfer mode, a target weight transfer value is set by a user via the driver terminal 80. Alternatively, the user may select a target value from a list of predetermined values. The ECU 16 controls the height of the front linkage 26 via the hydraulic control unit 44 so as to maintain the pressure in the first chamber 34a as near as possible to a value corresponding to the target weight transfer.

If, for example, the down-force pressure sensed by sensor 70 falls below a target value, ECU 16 commands a lowering of the front linkage 26. Conversely, if the down-force pressure sensed by sensor 70 rises above a target value or range, ECU 16 commands a raising of the front linkage 26.

Advantageously, by transferring a portion of the tractor's weight onto a front-mounted implement, the ground impact is spread over a wider area thus reducing soil compaction caused by passage of the tractor.

In an enhanced mode of operation, control of the weight transfer at the front linkage may be made a function of the sensed wheelslip of the tractor. By way of example, if the sensed wheelslip of the tractor rises above a threshold determined by a user or otherwise, then the ECU may enact a reduction in the weight transfcr by raising the front linkage until thc wheelslip falls below the threshold. This allows optimisation of the weight distribution upon the ground whilst minimising the wheelslip.

The weight transfer mode may be selectively activated and deactivated as required. Activation and deactivation may be automatic in response to raising and lowering of the implement at

field headlands for example.

Although the invention has been illustrated with a press, it is envisaged that other implements could be attached to the front linkage whilst remaining within the scope of the invention.

Although described above in relation to front linkage, it is envisaged that the weight transfer mode can instead, or additionally, be applied to a rear hitch providing the lifting/lowering of the lift arms is controlled by double-acting actuators.

Claims

CLAIMSI. A tractor hitch control system comprising a linkage assembly having a pair of lift arms for attachment to an implement and a lift actuator for controlling the height of the lift arms, the system further comprising means to measure the downward force exerted on the lift arms, wherein the hitch is operable in a weight transfer mode in which said downward force is controlled.
2. A control system according to Claim 1, wherein the lift actuator is a double-acting hydraulic cylinder.
3. A control system according to Claim 2, wherein the means to measure the downward force is a pressure sensor which measures the pressure on one side of a piston in the hydraulic cylinder.
4. A control system according to Claim 3, wherein a supply of pressurised fluid to the lift cylinder is controlled to maintain the downward force within a target range.
5. A control system according to Claim I, wherein the lift actuator comprises an electric motor.
6. A control system according to any preceding claim, wherein a target downward force is set by a user via a driver interface device.