Draft force detection on a vehicle having a linkage

1. A vehicle control system for a vehicle having a continuously variable transmission (CVT), for controlling a height of a linkage on the vehicle and/or on an implement coupled with the vehicle, in which the linkage is automatically raised and lowered depending on a draft force detected by the vehicle, wherein an input draft force detected by sensors in the CVT or a driveline is inputted into the control system and said system further processes said input draft force to provide an output draft force upon which movement of the linkage is based, wherein said control system processes the input draft force by at least one of the following:

compensating the input draft force detected during acceleration or deceleration,

compensating the input draft detected while travelling along a slope,

equalizing the input draft force by applying a ramp function, and

reducing the input draft force when the linkage is at a predetermined height.

2. The vehicle control system as claimed in claim 1 , wherein the input draft force detected during acceleration or deceleration is compensated by taking the draft force applied to the mass of the vehicle into account for a given acceleration/deceleration value.

3. The vehicle control system as claimed in claim 2 , wherein the mass of the vehicle is stored electronically and accessed by the control system.

4. The vehicle control system as claimed in claim 2 , wherein the mass of the vehicle can be varied by an operator.

5. The vehicle control system as claimed in claim 1 , wherein to compensate the input draft force while travelling along a slope, the control system receives an angle of the slope, calculates a component of a drag force for that angle and takes that component into account to determine the output draft force.

6. The vehicle control system as claimed in claim 1 , wherein the control system sets a maximum output draft force when the input draft force exceeds a pre-determined value and the maximum output draft force is ramped down when the linkage is moved above a pre-determined height.

7. The vehicle control system as claimed in claim 6 , wherein the pre-determined height is selected at a height where an attached implement cannot contact the ground.

8. An agricultural tractor comprising the vehicle control system as claimed in claim 1 .

9. A control method for a vehicle having a continuously variable transmission (CVT), the control method for controlling a height of a linkage on the vehicle and/or on an implement coupled with the vehicle, the control method comprising the steps of:

detecting an input draft force by sensors in the CVT or driveline;

processing said input draft force to provide an output draft force upon which movement of the linkage is based; and

raising and lowering the linkage based on the output draft force,

wherein the step of processing comprises at least one of the following:

compensating the input draft force detected during acceleration or deceleration,

compensating the input draft detected whilst travelling along a slope,

equalizing the input draft force by applying a ramp function, and

reducing the input draft force when the linkage is at a predetermined height.

10. A controller for a vehicle configured to carry out the method as claimed in claim 9 .

11. A computer program product comprising a non-transitory storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing the steps of the method as claimed in claim 9 .