Construction machine

Abstract

A construction machine has a hydraulic pump driven by a prime mover, a hydraulic motor, an electric motor, a storage device for delivering and receiving electric power to and from the electric motor, and a controller for exercising drive control of the electric motor. A speed reduction mechanism for transmitting drive forces of the electric motor and hydraulic motor to a swing structure is also provided. The controller includes inductive voltage waveform detecting means for detecting an inductive voltage waveform of the electric motor, and magnetic pole position computing means for, in a state where the swing structure is driven only by the torque of the hydraulic motor, taking in the inductive voltage waveform from the inductive voltage detecting means and computing a magnetic pole position of a rotor of the electric motor on the basis of the inductive voltage waveform and not via a rotation position sensor.

1 . A construction machine comprising:
 a prime mover;   a hydraulic pump driven by the prime mover;   a hydraulic motor driven by hydraulic fluid from the hydraulic pump;   an electric motor;   a storage device for delivering and receiving electric power to and from the electric motor;   a controller for electric motor control, the controller exercising drive control on the electric motor; and   a speed reduction mechanism for transmitting drive forces of the electric motor and the hydraulic motor to a swing structure;   wherein the controller for electric motor control includes   inductive voltage waveform detecting means for detecting an inductive voltage waveform of the electric motor; and   magnetic pole position computing means for, in a state where the swing structure is driven only by torque of the hydraulic motor, taking in the inductive voltage waveform from the inductive voltage waveform detecting means and computing a magnetic pole position of a rotor of the electric motor on the basis of the inductive voltage waveform obtained not via a rotation position sensor.   
     
     
         2 . The construction machine according to  claim 1 ,
 wherein when a magnetic pole position of a rotor with respect to a stator in the electric motor is unclear because of low swing speed of the swing structure, an swing control lever for swing-controlling the swing structure is operated to output a swing drive command to a control valve adapted to supply hydraulic fluid from the hydraulic pump to the hydraulic motor to drive the swing structure.   
     
     
         3 . The construction machine according to  claim 2 ,
 wherein the controller for electric motor control further includes sensor-less drive control means for, when the electric motor reaches a rotation speed that can be used for computing a magnetic pole position of the rotor, computing a magnetic pole position of the rotor on the basis of the inductive voltage waveform, and controlling drive of the electric motor.   
     
     
         4 . The construction machine according to  claim 3 ,
 wherein the sensor-less drive control means starts to apply torque to the electric motor when the electric motor is increased in speed to reach a set value.   
     
     
         5 . The construction machine according to  claim 3 ,
 wherein the sensor-less drive control means stops application of torque to the electric motor when the electric motor is reduced in speed to reach a set value.