Patent ID: 9624914
Date: 2017-04-18
CPC Classifications: F04B

Claim:
1. A hydraulic pump having a swash plate that can be installed obliquely inclined relative to a rotational shaft and a plurality of pistons whose axial displacement is defined by the swash plate and that rotate around the rotational shaft, comprising: the rotational shaft receiving input of torque that is output from an electric motor; a housing that rotatably supports the rotational shaft; a cylinder block that is installed inside the housing, is provided with a plurality of cylinder chambers extending parallel to the rotational shaft, and rotates with the rotational shaft; the pistons being supported relative to the respective cylinder chambers in the cylinder block so as to be slidably displaceable along a direction parallel to the rotational shaft; the swash plate coming into contact with ends of the pistons and being rotatable around the rotational shaft with the pistons, and being rotatable about a rotation centerline that is obliquely inclined relative to the rotational shaft; a case that is installed inside the housing and pivotably supported relative to the housing; a bearing portion that holds the swash plate relative to the case so as to be rotatable about the rotation centerline; and a piston biasing mechanism that is supported relative to the cylinder block and includes a spring that biases the pistons toward the swash plate, wherein the pistons reciprocate in the cylinder chambers with rotation of the rotational shaft, whereby the pressure of oil sucked into the cylinder chambers is raised and thereafter the oil is discharged, wherein the piston biasing mechanism includes: wherein each of the pistons has a piston shaft portion extending from inside the cylinder chamber and passing through a hole provided in the piston biasing plate, and a piston head portion disposed on a swash plate side relative to the piston biasing plate, the piston head portion being larger in diameter than the piston shaft portion having a constant diameter from a first point where the piston shaft portion extends from inside the cylinder chamber up to a second point where the piston shaft portion connects to the piston head portion, the diameter of the piston head portion is larger than the constant diameter of the piston shaft portion between the second point and a third point where the piston head portion has the largest diameter so that the piston head portion of each piston can be engaged with the piston biasing plate on a side opposite the cylinder block.