Main shaft two-stage speed changing box of single-spline-shaft double-shifting-fork machine tool

The utility model relates to a main shaft two-stage speed changing box of a single-spline-shaft double-shifting-fork machine tool, and belongs to the field of mechanical processing. The main shaft two-gear speed changing box comprises a main shaft motor, wherein the main shaft motor is fixedly connected with a spline shaft through a spline shaft supporting bearing; a first-stage input gear is arranged at the upper part of the spline shaft and is connected with a first-stage changing shifting fork; a second-stage input gear is arranged at the lower part of the spline shaft and is connected with a second-stage changing shifting fork; the first-stage changing shifting fork and the second-stage changing shifting fork are fixedly connected with shifting fork control rods respectively; shifting fork control rods oil cylinders are fixedly connected with the shifting fork control rods; an inner supporting bearing is arranged at the middle part of the spline shaft and is fixedly connected to a speed changing box shell through a supporting ribbed plate. According to the main shaft two-stage speed changing box, the two shifting forks replace the single shifting fork; besides, the supporting bearing is arranged at the middle part of the spline shaft, so that the supporting distance of the spline shaft is reduced, and the rigidity of a transmission chain is improved.