Method for operating a working machine, a working machine and a controller

Abstract

A working machine has working hydraulics comprising a pump. The working machine has an independent motor drive for powering the working hydraulics. a load on the working hydraulics is estimated based on a load estimation model using an actual motor power consumption of the independent motor drive. The estimated load is compared with a critical threshold. If the estimated load is above the critical threshold a warning signal or a control command stopping an actual movement is provided.

What is claimed is: 
     
         1 . A method for operating a working machine with working hydraulics comprising a pump, the working machine further comprising an independent motor drive for powering the working hydraulics comprising the steps
 estimating a load on the working hydraulics based on a load estimation model using an actual motor power consumption of the independent motor drive,   comparing the estimated load with a critical threshold,   if the estimated load is above the critical threshold providing a warning signal or a control command stopping an actual movement.   
     
     
         2 . The method according to  claim 1 , wherein the critical threshold is determined using information on orientation of the working machine and/or of the working hydraulics and/or information on a speed of the working machine, wherein information on orientation is preferably provided using inertial measurement units on the working machine. 
     
     
         3 . The method according to  claim 2 , wherein the information on orientation comprises boom, bucket and/or vehicle orientation. 
     
     
         4 . The method according to  claim 1 , wherein the load estimation model uses a pump flow rate (Q) delivered by the pump together with a motor speed (ω) and/or a current (I) and a voltage (V) of the independent motor drive to determine the estimated load. 
     
     
         5 . The method according to  claim 4 , wherein the pump flow rate (Q) is estimated using a known volume of the pump (V Opump ) and a rotational speed of the pump (n), wherein preferably the pump flow rate is estimated according to Q=V Opump ·n, wherein
 n is the rotational speed of the pump in rad/s and 
 V Opump  is the volume of the pump in m 3 . 
 
     
     
         6 . The method according to  claim 1 , wherein the load estimation model determines the estimated load using F/A=(T·ω/ηVo)·t or F/A=(V·I/Vo)·t, wherein
 F is force in N, 
 T is torque in Nm, 
 ω is motor speed in rad/s, 
 η is efficiency of the independent motor drive, 
 Vo is total volume delivered by the pump in m 3  and Vo=∫Q dt, 
 Q is working pump flow rate in m 3 /s 
 V is voltage in V, 
 I is current in A, 
 A is area over which force is applied in m 2 , 
 t is time in s. 
 
     
     
         7 . The method according to  claim 1 , wherein the load estimation model additionally uses working hydraulic oil temperature. 
     
     
         8 . The method according to  claim 7 , wherein based on the working hydraulic oil temperature a viscosity correction factor Kv is determined and based on the viscosity correction factor a corrected pump flow rate Qc is determined according Qc=Kv·Q 0 , wherein Q 0  is a standard pump flow rate at a defined standard temperature and wherein the corrected flow rate is used by the load estimation model as the pump flow rate. 
     
     
         9 . The method according to  claim 8 , wherein values for the viscosity correction factor Kv for different temperatures are determined using stored values, which are preferably determined in a previous step according to Kv=μ/μ0, wherein
 Kv is the viscosity correction factor, 
 μ is the actual viscosity in Pa·s at a certain temperature, 
 μ 0  is the reference viscosity at a standard temperature in Pa·s. 
 
     
     
         10 . A computer system for operating a working machine the computer system comprising a processing circuitry configured to perform the steps of the method according to  claim 1 . 
     
     
         11 . A computer program comprising program code means for performing the steps of the method according to  claim 1  when said program is executed by a processor device. 
     
     
         12 . A non-transitory computer-readable storage medium comprising instructions, which when executed by the processor device, causes the processor device to perform the method  claim 1 . 
     
     
         13 . A working machine with working hydraulics and an independent motor drive for powering the working hydraulics comprising a computer system according to  claim 10 . 
     
     
         14 . The working machine according to  claim 13 , wherein the working machine is a wheel loader.