a box, at which a large variable displacement ball connecting rod assembly and a small variable displacement ball connecting rod assembly are installed;

a multi-stage raceway bearing ring, which is embedded at one end of the box;

a multi-stage raceway ball hinge shaft, which is supported at the multi-stage raceway bearing ring, a plurality of ball hinges arranged in a circumferential direction at one end face of the multi-stage raceway ball hinge shaft;

a multi-stage rolling body retainer, which is arranged between the multi-stage raceway bearing ring and the multi-stage raceway ball hinge shaft, and in which rolling bodies are installed; wherein the rolling bodies, the multi-stage raceway bearing ring and the multi-stage raceway ball hinge shaft form a rolling bearing which is configured to have a self-centering operation performance mainly bearing an axial force;

a box shaft, which is installed in the box and located behind the multi-stage raceway ball hinge shaft;

a bush bearing ring, which is installed at a rear end of the box shaft and hinged with the large variable displacement ball connecting rod assembly;

a box end cap, which is installed in the box at an end that is not provided with the multi-stage raceway ball hinge shaft, an inner surface of the box end cap is an arc surface;

an oil distribution plate, wherein one end of the oil distribution plate is embedded with a suspension ring which is configured to provide a complete lubricating oil film at a partition wall for high and low pressures of the oil distribution plate, and which is further configured to prevent a hydraulic oil in a high pressure oil chamber of the oil distribution plate from flowing into a low pressure oil chamber; another end of the oil distribution plate is a circular arc surface that matches the arc surface of the box end cap; and a lower end of the oil distribution plate has a ball hinge, which forms a hinge with the small variable displacement ball connecting rod assembly;

a cylinder block, which is connected with the oil distribution plate through a needle bearing and a pin shaft of the oil distribution plate at an inner hole thereof; wherein a bearing ring is sleeved over an outer side of the cylinder block, is connected with the bush bearing ring through a retainer and rolling bodies, and is supported at the box shaft; a thrust bearing ring is installed at an end face of the cylinder block, and is supported at the oil distribution plate through a retainer and rolling bodies; a plurality of holes are provided in a circumferential direction of the cylinder block, and the number of the plurality of holes matches the number of the plurality of ball hinges of the multi-stage raceway ball hinge shaft; each hole comprises a corresponding linear bearing hole and plunger hole; each heavy-load linear rolling bearing is located within a corresponding linear bearing hole, and each plunger is located within a corresponding plunger hole; each plunger is installed therein with a plunger ball hinge, and each plunger is supported by the heavy-load linear rolling bearing; both ends of each heavy-load linear rolling bearing are assembled with reversers to multiply the number of raceways and improve a load-bearing density; and

a plurality of ball connecting rods, which are mated with the plurality of ball hinges of the multi-stage raceway ball hinge shaft; wherein one end of each ball connecting rod is press-fitted at the multi-stage raceway ball hinge shaft through a return disc, and forms a hinge with the corresponding ball hinge; the other end of each ball connecting rod is hinged with the plunger through the corresponding plunger ball hinge, fixed with a hole elastic stop ring through a nested sleeve in the plunger, and is integrally installed into an inner hole of the corresponding heavy-load linear rolling bearing and the interior of the plunger hole of the cylinder block.