Traveling hydraulic stepless transmission

A traveling hydraulic stepless transmission, comprising:

• a tank of hydraulic oil;
• a hydraulic pump of a variable displacement type;
• a capacity adjustment part disposed in the hydraulic pump;
• a hydraulic motor;
• a closed circuit that fluidly connects the hydraulic pump and the hydraulic motor in a closed circuit;
• and
• a pair of neutral check valves configured for replenishment of hydraulic oil that are disposed individually in each of a first oil passage and a second oil passage of the closed circuit,
• wherein each of the pair of check valves comprises:
• a valve housing that is a cylindrical housing;
• a first oil chamber formed on one end side of the valve housing in a cylinder axial direction;
• a second chamber formed on another end side of the valve housing in the cylinder axial direction;
• a communication hole connecting the first oil chamber and the second chamber;
• an opening to fluidly connect the first oil chamber to the first oil passage or the second oil passage;
• a first open hole to fluidly connect the second chamber to the tank;
• a cylindrical body inserted through the communication hole to be displaceable in the cylinder axial direction, wherein the cylindrical body is formed with an oil hole passing through in a axial direction of the cylindrical body, an orifice opened on an outer peripheral surface of the cylindrical body and communicating with the oil hole, and a first seat surface formed at an end portion on a side facing the first oil chamber;
• a spring member configured to bias the cylindrical body toward the first oil chamber;
• and
• a valve body housed in the first oil chamber,
• wherein the valve housing is formed with a second seat surface positioned on the first oil chamber side in the cylinder axial direction;
• wherein when a pressure in either the first oil passage or the second oil passage is equal to or less than the biasing force acting on the cylindrical body, the valve body of the corresponding neutral check valve is brought into pressure contact with the first seat surface and separated from the second seat surface by the cylindrical body being displaced to the first oil chamber side, and the first oil passage and the second oil passage are made to fluidly communicate with the tank through the orifice, and
• wherein when a pressure in the first oil passage or the second oil passage becomes higher than the biasing force of the spring member, the valve body of the corresponding neutral check valve is displaced to the second chamber side against the biasing force of the spring member, and is brought into pressure contact with the second seat surface, which shut off fluid communication between the a high pressure side of the first oil passage or the second oil passage and the tank.