Agricultural machine with variable RPM control

1. A self-propelled agricultural machine, comprising:

elements for at least one of gathering and processing crops;

an engine operable to travel the machine through a first driving mechanism and to drive the operation of said elements through a second driving mechanism; and

a control unit for controlling engine RPM,

wherein the control unit is configured to control the engine RPM to reach or at least lie within a restricted sector around a target RPM, which is in turn based on an assessment of an imposed engine load, wherein the control unit is programmed in:

a low load range to hold the target RPM at a constant target value;

at least one medium load range for the target RPM to be determined as a continuously rising function of the load; and

a high load range to determine the RPM from a torque curve of the engine.

2. An agricultural machine according to claim 1 , wherein the imposed engine load is derived from a measurement of the engine RPM and of fuel consumption.

3. An agricultural machine according to claim 1 , wherein a current RPM and the imposed engine load are assessed and communicated by a second control unit.

4. An agricultural machine according to claim 1 , wherein a rate of change of the target RPM within said medium load range is itself a rising function of the extent to which the imposed load either respectively exceeds the an upper limit of the medium load range or undershoots a lower limit of the medium load range.

5. An agricultural machine according to claim 1 , wherein the at least one medium range comprises a lowest medium load range and a non-overlapping higher medium load range, the control unit is configured to keep an RPM equal to a constant target values within the medium load ranges, the lowest medium load range beginning at 0% of said range, and wherein:

said constant target value is lowest for the lowest of medium load range and rises for a higher medium load range,

in a transition zone between the lowest and a higher medium load range of constant target value the target RPM is a continuously rising function of the engine load.

6. An agricultural machine according to claim 4 , wherein a difference between constant target values of two neighbouring medium load ranges is constant.

7. An agricultural machine according to claim 1 wherein a machine operator sets engine RPM corresponding to a medium load range having a constant setting, or an RPM between two medium load ranges with a continuously rising target value.

8. An agricultural machine according to claim 1 , the control unit is programmed further in:

a transition zone between the at least one medium load range and the high load range, where the control unit raises the target RPM continuously to a maximum value; and

wherein in the high load range the control unit controls the target RPM at maximum value and the RPM of the engine is determined by the torque curve of said engine.

9. A method of controlling the RPM of a machine using at least one programmed control unit, the control unit is configured to perform the steps of:

assessing the imposed engine load; and

controlling the engine RPM to reach or at least lie within a restricted sector around a target RPM, which is in turn based on an assessment of an imposed engine load, wherein the control unit is programmed in:

a low load range where the target RPM remains at a constant target value;

at least one medium load range where the target RPM is a continuously rising function of the load; and

a high load range where the RPM is determined by the torque curve of the engine.

10. An agricultural machine according to claim 9 , wherein a rate of change of the target RPM within said at least one medium load range is itself a rising function of the extent to which the imposed load respectively exceeds the at least one medium load range upper limit or undershoots the at least one medium load range lower limit.