Patent ID: 9702379
Date: 2017-07-11
CPC Classifications: B60K,B60W,E02F,F15B,Y02T

Claim:
1. A hybrid working machine comprising: an engine; a hydraulic pump driven by the engine; a motor which drives the hydraulic pump in combination with the engine; a plurality of actuators driven by hydraulic fluid delivered by the hydraulic pump; a pilot pump driven by the engine; a pilot hydraulic power source connected to the pilot pump to generate a pilot primary pressure based on delivery fluid from the pilot pump; an engine revolution speed detection valve interposed between the pilot pump and the pilot hydraulic power source, the engine revolution speed detection valve further generating a hydraulic signal as an absolute pressure dependent on an engine revolution speed of the engine based on the delivery fluid from the pilot pump, and outputting the hydraulic signal; a maximum load pressure detection circuit which detects a maximum load pressure of the plurality of actuators; a plurality of flow control valves which control respective flow rates and directions of hydraulic fluid supplied from the hydraulic pump to the plurality of actuators; a plurality of pressure compensating valves which control respective differential pressures across the plurality of flow control valves to be equal to a differential pressure between a delivery pressure of the hydraulic fluid supplied from the hydraulic pump and the maximum load pressure; and a pump control system including a torque control unit which performs control to reduce a displacement of the hydraulic pump when the delivery pressure of the hydraulic pump is being raised, so that an absorption torque of the hydraulic pump will not exceed a predetermined maximum torque, and a load sensing control unit which controls the displacement of the hydraulic pump in such a manner that the delivery pressure of the hydraulic pump becomes higher than the maximum load pressure by a target differential pressure, wherein the hydraulic signal output from the engine revolution speed detection valve is received by the load sensing control unit as the target differential pressure for load sensing control, and the load sensing control unit includes a load sensing control piston that controls the displacement of the hydraulic pump by driving a displacement volume varying member of the hydraulic pump based on a pilot primary pressure of the pilot hydraulic power source; a plurality of pressure sensors including a first pressure sensor which detects the delivery pressure of the hydraulic pump, second pressure sensor which detects the differential pressure between the delivery pressure of the hydraulic pump and the maximum load pressure, and a third pressure sensor which detects the hydraulic signal output from the engine revolution speed detection valve, and a control system configured to receive the detected pressures from the first, second, and third pressure sensors, and control the motor; wherein the control system is further configured to: store a predetermined constant pressure of the pilot hydraulic power source, calculate the displacement of the hydraulic pump based on the detected pressures from the first, second, and third pressure sensors, the constant pressure of the pilot hydraulic power source, and an equation of motion about the displacement volume varying member of the hydraulic pump, calculate the engine revolution speed based on the hydraulic signal detected with the third pressure sensor, calculate a power need of the hydraulic pump based on the engine revolution speed, the calculated displacement of the hydraulic pump, and the delivery pressure of the hydraulic pump detected with the first pressure sensor, calculate an output power of the engine based on the engine revolution speed, and switch between powering control and generation control of the motor in accordance with a result of comparing the power need of the hydraulic pump and the output power of the engine.