Hybrid system for construction machine

Abstract

When the actuator drive torque of a hydraulic pump is lower than a switching torque τ0, a controller closes a solenoid switching valve and makes a rotary electric machine function as a generator. With the increase in the actuator drive torque, the controller controls a pressure compensated flow control valve so that the flow rate of hydraulic fluid supplied from the hydraulic pump to a rotary hydraulic device decreases. When the actuator drive torque is higher than the switching torque, the controller opens the solenoid switching valve, makes the rotary electric machine function as an electric motor, and controls the pressure compensated flow control valve so that the hydraulic fluid discharged by the hydraulic pump is not supplied to the rotary hydraulic device. Consequently, shocks due to flow rate fluctuation are prevented when operational states of the rotary hydraulic device and the rotary electric machine are switched.

1 . A hybrid system for a construction machine, comprising:
 an engine;   a main hydraulic pump which is driven by the engine;   a plurality of actuators;   a control valve which is connected to the main hydraulic pump via a first hydraulic fluid supply line for controlling the flow of hydraulic fluid supplied to the actuators;   a rotary electric machine which has functions of both an electric motor and a generator;   a rotary hydraulic device which is connected to the rotary electric machine, driven by the rotary electric machine and functions as a hydraulic pump when the rotary electric machine functions as an electric motor, and functions as a hydraulic motor and drives the rotary electric machine when the rotary electric machine functions as a generator;   a second hydraulic fluid supply line which connects the rotary hydraulic device to the first hydraulic fluid supply line;   an electricity storage device; and   a bidirectional converter which is connected between the electricity storage device and the rotary electric machine for controlling the transfer of electric power between the electricity storage device and the rotary electric machine, wherein:   the hybrid system comprises:
 a flow control valve device which is arranged in the first hydraulic fluid supply line and in the second hydraulic fluid supply line for controlling the ratio between the flow rate of the hydraulic fluid supplied to the control valve and the flow rate of the hydraulic fluid supplied to the rotary hydraulic device when the hydraulic fluid discharged by the main hydraulic pump is supplied to the rotary hydraulic device via the second hydraulic fluid supply line; 
 a third hydraulic fluid supply line which connects the rotary hydraulic device to the first hydraulic fluid supply line downstream of the flow control valve device; 
 a first switching valve which is provided in the third hydraulic fluid supply line to be capable of opening and closing; 
 a drive torque detecting device which detects drive torque of the main hydraulic pump; and 
 a control device which judges whether actuator drive torque for driving the actuators is higher than preset switching torque or not based on the drive torque of the main hydraulic pump detected by the drive torque detecting device, and 
   when the actuator drive torque is equal to or lower than the switching torque, the control device switches the first switching valve to its closed position and controls the bidirectional converter so that the rotary electric machine functions as a generator, while also controlling the flow control valve device so that the flow rate of the hydraulic fluid supplied from the main hydraulic pump to the rotary hydraulic device decreases with the increase in the actuator drive torque, and   when the actuator drive torque is higher than the switching torque, the control device switches the first switching valve to its open position, makes the rotary hydraulic device function as a hydraulic pump by controlling the bidirectional converter so that the rotary electric machine functions as an electric motor, and controls the flow control valve device so that the hydraulic fluid discharged by the main hydraulic pump is not supplied to the rotary hydraulic device.   
     
     
         2 . The hybrid system for a construction machine according to  claim 1 , wherein:
 the flow control valve device includes:
 a throttle part which is provided in the second hydraulic fluid supply line; and 
 a pressure compensated flow control valve which is arranged in the first hydraulic fluid supply line and in the second hydraulic fluid supply line, the pressure compensated flow control valve having a pressure compensation function of controlling the flow rate of the hydraulic fluid supplied to the rotary hydraulic device by controlling differential pressure across the throttle part when the hydraulic fluid discharged by the main hydraulic pump is supplied to the rotary hydraulic device via the second hydraulic fluid supply line, the pressure compensated flow control valve supplying the control valve with a flow of the hydraulic fluid corresponding to a demanded flow rate in priority to the throttle part when the control valve is operated, and 
   when the actuator drive torque is equal to or lower than the switching torque, the control device controls the pressure compensated flow control valve so that the differential pressure across the throttle part and the flow rate of the hydraulic fluid supplied to the rotary hydraulic device decrease with the increase in the actuator drive torque.   
     
     
         3 . The hybrid system for a construction machine according to  claim 2 , wherein:
 the pressure compensated flow control valve includes:
 a first pressure-receiving part for action in an opening direction, to which hydraulic pressure on the upstream side of the throttle part is lead via a first signal hydraulic fluid line; and a second pressure-receiving part for action in a throttling direction, to which hydraulic pressure on the downstream side of the throttle part is lead via a second signal hydraulic fluid line; when the rotary hydraulic device functions as a hydraulic motor, and 
   the control device includes:
 a second switching valve which is arranged in the second signal hydraulic fluid line; and 
 a controller which receives a signal inputted from the drive torque detecting device, and 
   when the actuator drive torque is equal to or lower than the switching torque, the controller validates the pressure compensation function of the pressure compensated flow control valve by switching the second switching valve to a first position for leading the hydraulic pressure on the downstream side of the throttle part to the second pressure-receiving part, and   when the actuator drive torque higher than the switching torque, the controller invalidates the pressure compensation function of the pressure compensated flow control valve by switching the second switching valve to a second position for connecting the second pressure-receiving part with a tank.   
     
     
         4 . The hybrid system for a construction machine according to  claim 2 , wherein:
 the pressure compensated flow control valve includes:
 a first pressure-receiving part for action in an opening direction, to which hydraulic pressure on the upstream side of the throttle part is lead via a first signal hydraulic fluid line; a second pressure-receiving part for action in a throttling direction, to which hydraulic pressure on the downstream side of the throttle part is lead via a second signal hydraulic fluid line; and a third pressure-receiving part which sets a target compensation differential pressure according to control pressure; when the rotary hydraulic device functions as a hydraulic motor, and 
   the control device includes:
 a solenoid proportional pressure reducing valve which outputs the control pressure to the third pressure-receiving part; and 
 a controller which receives a signal inputted from the drive torque detecting device, and 
   the controller calculates target compensation differential pressure that decreases with the increase in the actuator drive torque and equals 0 when the actuator drive torque exceeds the switching torque, and controls the solenoid proportional pressure reducing valve so that the target compensation differential pressure is achieved.   
     
     
         5 . The hybrid system for a construction machine according to  claim 1 , wherein the control device determines a torque value by subtracting the generator torque of the rotary electric machine functioning as a generator from the bidirectional converter from the drive torque of the main hydraulic pump detected by the drive torque detecting device, and uses the torque value as the actuator drive torque. 
     
     
         6 . The hybrid system for a construction machine according to  claim 1 , wherein the drive torque detecting device is a torque sensor which is provided on a rotating shaft transmitting driving force of the engine to the main hydraulic pump. 
     
     
         7 . The hybrid system for a construction machine according to  claim 2 , wherein the drive torque detecting device is a torque sensor which is provided on a rotating shaft ( 2 ) transmitting driving force of the engine to the main hydraulic pump. 
     
     
         8 . The hybrid system for a construction machine according to  claim 3 , wherein the drive torque detecting device is a torque sensor which is provided on a rotating shaft transmitting driving force of the engine to the main hydraulic pump. 
     
     
         9 . The hybrid system for a construction machine according to  claim 4 , wherein the drive torque detecting device is a torque sensor which is provided on a rotating shaft transmitting driving force of the engine to the main hydraulic pump. 
     
     
         10 . The hybrid system for a construction machine according to  claim 5 , wherein the drive torque detecting device is a torque sensor which is provided on a rotating shaft transmitting driving force of the engine to the main hydraulic pump.