Piston pump and piston motor

A piston pump, comprising a cylinder body, a piston, a main shaft, and an oil dispensing mechanism;

• wherein the cylinder body is arranged coaxially with the main shaft and is fixed in place relative to the main shaft by a housing mounted outside the cylinder body, and an end cover;
• the piston is reciprocally mounted in a cylinder bore of the cylinder body, and is configured to move along the cylinder bore;
• opposing axial ends of the cylinder body are sealed by the end cover;
• the oil dispensing mechanism comprises an oil suction mechanism and an oil discharging mechanism;
• a roller is mounted on the piston, and the roller is rotatablely connected to the piston;
• a driving wheel is arranged on the main shaft;
• the driving wheel is mounted in cooperation with the main shaft, or the driving wheel is integrally formed with the main shaft;
• and a driving groove is formed on the driving wheel, and a roller-path surface of the driving groove is a curved surface;
• a size of the driving groove is adapted to an outer diameter of the roller;
• the main shaft rotates to drive the driving wheel to rotate to further drive the piston-to move along the cylinder bore.