Road finisher and method for controlling its operation

Abstract

A road finisher comprises a tractor, a material hopper configured to receive material, and a screed mounted to the tractor by towing arms so as to be pivotable around a towing point. The road finisher further comprises a control system comprising a height detection device configured to detect vertical movements of the screed with respect to a height reference and, to generate a height signal based on the detected movements, and an adjusting cylinder connected to the tractor and one of the towing arms and being configured to adjust a height of the towing point relative to the tractor. The control system is configured to compare the height signal to a target value and thereby calculate a control deviation, to limit an adjustment displacement of the adjusting cylinder to a maximum value based on the control deviation, wherein the maximum value is proportional to the control deviation.

What is claimed is: 
     
         1 . A road finisher, comprising:
 a tractor;   a material hopper, which is disposed at a front of the tractor as seen in a driving direction and which is configured to receive material;   a screed, which is mounted to the tractor by towing arms so as to be pivotable around a towing point, such that the screed is towable behind the tractor as seen in the driving direction; and   a control system comprising a height detection device, which is configured to generate a height signal, and an adjusting cylinder, the adjusting cylinder being connected to the tractor and one of the towing arms and being configured to adjust a height of the towing point relative to the tractor;   wherein the control system is configured to compare the height signal to a target value and thereby calculate a control deviation, to limit an adjustment displacement of the adjusting cylinder to a maximum value based on the control deviation, wherein the maximum value is proportional to the control deviation, and the control system is further configured to adjust the adjusting cylinder based on the control deviation and taking the maximum value into account.   
     
     
         2 . The road finisher according to  claim 1 , wherein the height detection device is configured to detect vertical movements of the screed with respect to a height reference and generate the height signal based on the detected movements. 
     
     
         3 . The road finisher according to  claim 1 , wherein the maximum value is defined relative to a reference value. 
     
     
         4 . The road finisher according to  claim 3 , wherein the reference value is adjustable by an operator. 
     
     
         5 . The road finisher according to  claim 3 , wherein the control system is configured to automatically adapt the reference value. 
     
     
         6 . The road finisher according to  claim 1 , wherein the maximum value is given by multiplication of the control deviation by a proportionality factor. 
     
     
         7 . The road finisher according to  claim 6 , wherein the proportionality factor is adjustable. 
     
     
         8 . The road finisher according to  claim 1 , wherein a top limit is defined for the maximum value. 
     
     
         9 . The road finisher according to  claim 1 , wherein the height detection device is configured to detect a movement of the screed with respect to a height reference and generate the height signal based on the detected movement. 
     
     
         10 . A method for controlling operation of a road finisher, which comprises a tractor, a material hopper disposed at a front of the tractor as seen in a driving direction and which is configured to receive material, a screed mounted to the tractor by towing arms so as to be pivotable around a towing point, such that the screed is towable behind the tractor as seen in the driving direction, a control system having a height detection device and an adjusting cylinder connected to the tractor and one of the towing arms, the method comprising:
 generating a height signal by the height detection device;   calculating a control deviation by comparing the height signal to a target value;   limiting an adjustment displacement of the adjusting cylinder to a maximum value, which is proportional to the control deviation;   calculating an adjustment signal based on the control deviation taking the maximum value for the adjustment displacement into account; and   adjusting a height of the towing point by the adjusting cylinder based on the adjustment signal.   
     
     
         11 . The method according to  claim 10 , further comprising detecting a movement of the screed with respect to a height reference by the height detection device, wherein the height signal is generated based on the detected movement of the screed with respect to the height reference. 
     
     
         12 . The method according to  claim 10 , wherein the maximum value is defined relative to a reference value. 
     
     
         13 . The method according to  claim 12 , wherein the reference value is adjustable by an operator. 
     
     
         14 . The method according to  claim 12 , further comprising automatically adapting the reference value by the control system. 
     
     
         15 . The method according to  claim 10 , wherein the maximum value is given by multiplication of the control deviation by a proportionality factor. 
     
     
         16 . The method according to  claim 15 , wherein the proportionality factor is adjustable. 
     
     
         17 . The method according to  claim 10 , wherein a top limit is defined for the maximum value.