Spline joints and methods of installing the same. A spline joint may include a box and a pin each having a hollow cylindrical body. The pin may be received by the box. The spline joint may further include splines received by a first set of grooves of the box and grooves of the pin. The splines may be insertable between the first set of grooves through a first set of slots of the box to join the box and the pin. The spline joint may further include at least one O-ring to be received by a second set of grooves of the box to create a seal between the box and the pin. The spline joint may further include a key configured to be received by a second slot of the box and installed in a slot of the pin.

A motor connection structure may be configured for coupling a rotor of a motor and an engine clutch retainer in the hybrid transmission. An example motor connection structure includes a damping unit coupled to an outer circumferential surface of the retainer in an axial direction of the rotor on an inner side of the rotor and supporting each of (i) the outer circumferential surface of the retainer, (ii) an inner circumferential surface of the rotor, and (iii) a coupled portion of the retainer.

Disclosed is an engine clutch motor connection structure for a hybrid transmission. The motor connection structure may be configured for coupling a rotor of a motor and an engine clutch retainer in the hybrid transmission. An example motor connection structure includes a damping unit coupled to an outer circumferential surface of the retainer in an axial direction of the rotor on an inner side of the rotor and supporting each of (i) the outer circumferential surface of the retainer, (ii) an inner circumferential surface of the rotor, and (iii) a coupled portion of the retainer.

A shaft mounting assembly includes an elongate shaft with an outer surface having a substantially circular cross-section and a cylinder having an inner surface defining a bore housing the shaft. A spring having a substantially circular discontinuous band with correspondingly shaped axially arcuate inner and outer surfaces. One of the surfaces comprises a groove, and the spring is positioned in the groove with both axial edges of the band located therein. In a de-energised state of the spring, the height of the band is greater than the depth of the groove, a portion of the band between the axial edges protruding out of the groove, the axial width of the band being less than the width of the groove; and, an energised state with the spring compressed within the bore to reduce the height of the band and increase the axial width compared to the de-energised state.