Patent ID: 9593467
Date: 2017-03-14
CPC Classifications: E02F,F04B,F15B

Claim:
1. An engine assist device in which a variable capacity type main pump is driven by an engine, excess energy generated when a fluid pressure actuator which is operated by a pressurized fluid discharged from the main pump is braked is accumulated in an accumulator, and energy is regenerated in the engine, the engine assist device comprising: a variable capacity type assist pump which is directly connected to the engine or the main pump and has a motor function for assisting an engine and a pump function for accumulating a pressure in an accumulator; a main accumulator which accumulates a pressurized fluid discharged from the assist pump; a sub-accumulator which temporarily pressure-accumulates a return pressure oil flowing out from the fluid pressure actuator and supplies the return pressure oil to the assist pump and the main accumulator; engine speed setting means for indicating a set engine speed; an engine speed sensor for detecting an actual engine speed; a main pump pressure sensor for detecting a main pump pressure during a discharging operation of the main pump; a main pump capacity sensor which detects a variable capacity of the main pump; a main accumulator pressure sensor which detects a main accumulator pressure of the main accumulator; a sub-accumulator pressure sensor which detects a sub-accumulator pressure of the sub-accumulator; an assist pump pressure sensor which detects an assist pump discharge pressure of a fluid discharged from the assist pump; a controller which obtains an engine load torque from the main pump pressure and the capacity of the main pump, wherein when the engine load torque exceeds assist starting torque set by the engine speed setting means, the controller calculates and controls a capacity of the assist pump based on a difference in torque between the engine load torque and the assist starting torque and a differential pressure between the main accumulator pressure and the assist pump discharge pressure, and introduces a pressure-accumulated fluid discharged from the main accumulator into the assist pump, and when the engine load torque is lower than charge starting torque set by the engine speed setting means, the controller calculates and controls the capacity of the assist pump based on a difference in torque between the engine load torque and the charge starting torque and a differential pressure between the assist pump discharge pressure and the sub-accumulator pressure, and introduces a pressurized fluid discharged from the assist pump into the main accumulator.