Method for controlling the elevation of a retaining device of a ground milling machine, and ground milling machine

Abstract

A method for controlling the elevation of a retaining device of a ground milling machine as well as to a ground milling machine. Essential for the invention is that the retaining device is held in an initial position at a distance from the underlying ground and is reset from a yield position.

What is claimed is: 
     
         1 . A method for controlling the elevation of a retaining device of a ground milling machine, comprising the steps:
 a) holding the retaining device in an initial position at a defined holding distance above the underlying ground, so that the retaining device is not in contact with the underlying ground;   b) starting the milling operation;   c) if ground material presses against the underside of the retaining device from below with a vertical upward counterforce, maintaining the retaining device in the initial position with a retaining force up to a defined maximum retaining force;   d) if the counterforce exceeds the maximum retaining force, releasing the retaining device for vertical upward displacement and a pushing of the retaining device upwards by the counterforce; and   e) returning the retaining device towards the initial position when the counterforce falls below the maximum retaining force, wherein the retaining device is returned no farther than to the initial position of the retaining device.   
     
     
         2 . The method according to  claim 1 , wherein at least one of the following steps precedes step a):
 placing the retaining device on the underlying ground and subsequently raising the retaining device until the initial position at the defined holding distance of the retaining device from the underlying ground is reached;   measuring an operating variable associated with the height adjustment of the retaining device and setting the raised height of the retaining device until a target value of the operating variable associated with the height adjustment of the retaining device is reached that corresponds to a reaching of the defined holding distance of the initial position;   measuring a distance variable that changes with the height adjustment of the retaining device in relation to the underlying ground and raising or lowering the retaining device until a distance variable is reached that corresponds to the defined holding distance of the initial position; and   deriving an actual raised state of the retaining device with the aid of displacement sensors associated with lifting columns for traveling devices and/or with the aid of a displacement sensor associated with a lifting device of the retaining device and/or with the aid of a position sensor of the ground milling machine, and raising or lowering the retaining device until a target raised state of the retaining device is reached that corresponds to the defined holding distance of the initial position and/or until a target displacement value of the displacement sensor associated with the lifting device of the retaining device is reached that corresponds to the defined holding distance of the initial position while considering measurement data of the position sensor of the ground milling machine.   
     
     
         3 . The method according to  claim 1 , wherein a pressure force acting in the vertical downward direction is actively applied in step c) in addition to the weight of the retaining device in order to hold the retaining device in the initial position at a defined holding distance above the underlying ground. 
     
     
         4 . The method according to  claim 1 , wherein step d) comprises switching a pressure relief valve. 
     
     
         5 . The method according to  claim 1 , wherein when there is a height adjustment of lifting columns connecting traveling devices to the machine frame, the elevation of at least one lifting column is monitored, in that a correction factor is determined if the elevation of the at least one lifting column is changed, and in that the correction factor is used to adapt the position of the retaining device in order to maintain the defined holding distance. 
     
     
         6 . The method according to  claim 1 , wherein the retaining device is held in the initial position so that the defined holding distance above the underlying ground lies in a range of from 5 to 50 mm. 
     
     
         7 . A ground milling machine for carrying out the method according to  claim 1 , comprising:
 a machine frame supported by traveling devices;   an operating platform, from which the ground milling machine is operated;   a milling device with a milling drum which is arranged inside a milling drum housing and which is rotatable about a rotation axis;   a retaining device which is arranged in front of the milling drum in the milling direction and which is height-adjustable via an actuator;   a drive engine, with which the drive power required for the milling and traveling operation is generated;   
       wherein
 a positioning control unit is provided which regulates the actuator of the retaining device in such a manner:
 that it initially maintains the elevation of the retaining device in an initial position at a defined holding distance above the underlying ground during milling operation, so that the retaining device is not in contact with the underlying ground; 
 that it keeps the retaining device in the initial position with a retaining force up to a defined maximum retaining force when ground material presses against the underside of the retaining device with a vertical upward counterforce from below; 
 that it releases the retaining device for vertical upward displacement when the counterforce exerted on the retaining device by the ground material exceeds the maximum retaining force; and 
 
 that it returns the retaining device towards, but no farther than, the initial position when the counterforce falls below the maximum retaining force. 
 
     
     
         8 . The ground milling machine according to  claim 7 , wherein the positioning control unit comprises a setting mode so as to comprise at least one of the following features for raising the retaining device to the initial position:
 it uses an elevation of the retaining device when the retaining device is lowered to the underlying ground; and/or   it incorporates measuring an operating variable associated with the height adjustment of the retaining device and setting the raised height of the retaining device until a target value of the operating variable associated with the height adjustment of the retaining device is reached that corresponds to the reaching of the defined holding distance; and/or   it incorporates measuring a distance variable that changes with the height adjustment of the retaining device in relation to the underlying ground and raising or lowering the retaining device until a distance variable is reached that corresponds to the defined holding distance;   it incorporates deriving an actual raised state of the retaining device with the aid of displacement sensors associated with lifting columns for traveling devices and/or with the aid of a displacement sensor associated with a lifting device of the retaining device and/or with the help of a position sensor of the ground milling machine.   
     
     
         9 . The ground milling machine according to any one of  claim 7 , wherein it has a display device on the operating platform of the ground milling machine, which displays at least one of the following operating states:
 the retaining device is in its initial position;   the retaining device is in contact with the ground;   the retaining device is pushed upward beyond its initial position.   
     
     
         10 . The ground milling machine according to  claim 7 , wherein it has a setting device on the operating platform of the ground milling machine, with which at least one of the following settings can be performed:
 setting the initial position of the retaining device;   setting the maximum retaining force;   switching between a ground contact mode and an initial position holding mode.