Hybrid driven hydraulic work machine

1. A hybrid-driven hydraulic work machine comprising an engine ( 7 ), a hydraulic pump ( 6 ) of the variable displacement type which is driven and rotated by the engine ( 7 ), an electric assist motor ( 10 ) which is linked to the engine ( 7 ) and the hydraulic pump ( 6 ), a plurality of actuators ( 3 a - 3 f ) which are driven by hydraulic fluid delivered from the hydraulic pump ( 6 ), and a plurality of operation devices ( 4 a , 4 b ) having operation members and outputting operation signals corresponding to operations on the operation members to cause the actuators to operate, wherein the hybrid-driven hydraulic work machine comprises:

revolution speed detection means ( 23 ) which detects revolution speed of the engine ( 7 );

a storage device ( 11 e ) which has stored a preset engine setup revolution speed of the engine ( 7 );

target engine revolution speed calculation means ( 11 a ) which sets a target revolution speed of the engine ( 7 ) at the engine setup revolution speed stored in the storage device ( 11 e );

engine control means ( 21 a ) which controls the revolution speed of the engine ( 7 ) based on the target revolution speed of the engine ( 7 );

engine load calculation means ( 11 b ) which calculates an engine load based on an engine torque signal from the engine control means ( 21 a ); and

at least one selected from the following:

electric motor power running calculation means ( 11 c ) which calculates a differential revolution speed between the target engine revolution speed and the revolution speed of the engine and performs power running control on the electric assist motor ( 10 ) depending on the differential revolution speed when the engine load is a prescribed value or higher; and

hydraulic pump absorption torque calculation means ( 11 d ) which performs reduction control on absorption torque of the hydraulic pump ( 6 ) depending on the differential revolution speed when the engine load is a prescribed value or higher.

2. A hybrid-driven hydraulic work machine comprising an engine ( 7 ), a hydraulic pump ( 6 ) of the variable displacement type which is driven and rotated by the engine ( 7 ), an electric assist motor ( 10 ) which is linked to the engine ( 7 ) and the hydraulic pump ( 6 ), a plurality of actuators ( 3 a - 3 f ) which are driven by hydraulic fluid delivered from the hydraulic pump ( 6 ), and a plurality of operation devices ( 4 a , 4 b ) having operation members and outputting operation signals corresponding to operations on the operation members to cause the actuators to operate, wherein the hybrid-driven hydraulic work machine comprises:

revolution speed detection means ( 23 ) which detects revolution speed of the engine ( 7 );

a storage device ( 11 e ) which has stored a preset engine setup revolution speed of the engine ( 7 );

target engine revolution speed calculation means ( 11 a ) which sets a target revolution speed of the engine ( 7 ) at the engine setup revolution speed stored in the storage device ( 11 e );

engine control means ( 21 a ) which controls the revolution speed of the engine ( 7 ) based on the target revolution speed of the engine ( 7 ); and

at least one selected from the following:

target electric motor revolution speed calculation means ( 71 a ) which sets a particular revolution speed within the target revolution speed of the engine ( 7 ) set by the target engine revolution speed calculation means ( 11 a ) as a target revolution speed of the electric assist motor ( 10 ) and electric motor power running calculation means ( 71 b ) which calculates a differential revolution speed between the target electric motor revolution speed and the revolution speed of the engine ( 7 ) and performs power running control on the electric assist motor ( 10 ) depending on the differential revolution speed when the revolution speed of the engine ( 7 ) has fallen below the target revolution speed of the electric assist motor ( 10 ); and

target hydraulic pump revolution speed calculation means ( 71 c ) which sets a particular revolution speed within the target revolution speed of the engine ( 7 ) set by the target engine revolution speed calculation means ( 11 a ) as a target revolution speed of the hydraulic pump ( 6 ) and hydraulic pump absorption torque calculation means ( 71 d ) which calculates a differential revolution speed between the target hydraulic pump revolution speed and the revolution speed of the engine ( 7 ) and performs reduction control on absorption torque of the hydraulic pump ( 6 ) depending on the differential revolution speed when the revolution speed of the engine ( 7 ) has fallen below the target revolution speed of the hydraulic pump ( 6 ).

3. The hybrid-driven hydraulic work machine according to claim 1 , wherein when the value of the engine load calculated by the engine load calculation means ( 11 b ) falls below a maximum value at the revolution speed of the engine ( 7 ) or a prescribed value in the vicinity of the maximum value, at least one selected from the following is executed:

cancellation of the power running control of the electric assist motor ( 10 ) by the electric motor power running calculation means ( 11 c ); and

cancellation of the reduction control of the absorption torque of the hydraulic pump ( 6 ) by the hydraulic pump absorption torque calculation means ( 11 d ).

4. The hybrid-driven hydraulic work machine according to claim 2 , wherein at least one selected from the following is executed:

cancellation of the power running control of the electric assist motor ( 10 ) by the electric motor power running calculation means ( 71 b ) when the revolution speed of the engine ( 7 ) exceeds the target electric motor revolution speed by a prescribed value or more; and

cancellation of the reduction control of the absorption torque of the hydraulic pump ( 6 ) by the hydraulic pump absorption torque calculation means ( 71 d ) when the revolution speed of the engine ( 7 ) exceeds the target hydraulic pump revolution speed by a prescribed value or more.