A method of lubricating a coupling shaft of a gear pump includes communicating lubricant from a first gear stage along a first splined end section of the coupling shaft and through a first slot in a first radial shoulder of the coupling shaft, and also communicating lubricant from a second gear stage along a second splined end section of the coupling shaft and through a second slot in a second radial shoulder of the coupling shaft. The first radial shoulder is axially spaced from the second radial shoulder by an axial distance SA along an axis of rotation of the coupling shaft. The first and second slots each define a lowermost radial dimension SR from the axis of rotation, with a ratio SR/SA of 0.25-0.77.

A fuel pump includes: an outer gear having a plurality of inner teeth; an inner gear having a plurality of outer teeth and eccentrically meshing with the outer gear; and a pump housing that defines a cylindrical gear housing chamber housing the outer gear and the inner gear to be rotatable. The outer gear and the inner gear rotate, while expanding and contracting a volume of a plurality of pump chambers formed between the outer gear and the inner gear, to sequentially draw fuel into and discharge from the pump chamber. An inner circumference part of the pump housing has a radially-inside corner part opposing a radially-outside corner part of an outer circumference part of the outer gear, and the pump housing has an annular groove formed in an annular shape all around the radially-inside corner part.

Invention provides gear pump bearing block and method of manufacturing gear pump bearing block. Bearing block includes a bush formed of antifriction alloy, bush having cylindrical portion providing bore adapted to receive bearing shaft of gear of pump, and further having flange portion extending radially outwardly at end of cylindrical portion to provide thrust face adapted to slidingly engage with side surface of gear. Bearing block also has backing layer covering radially outer surface of cylindrical portion and rear face of flange portion, backing layer being formed of less dense alloy compared to antifriction alloy. Furthermore, there is an annular gallery embedded in flange portion such that gallery is spaced from surface of bore and from thrust face, gallery surrounding bore, with inlet to and outlet from annular gallery such that, in use, fluid flows from inlet, through annular gallery to provide cooling of thrust face, and then to outlet.

A two stage pump (2, 4), where the high pressure stage (4) is a gear pump (11, 12), comprises a driving of the other stage (2) by a support shaft (74), mounted in the driven pinion (12), the shaft (74) being driven by the drive shaft (21), by means of a pair of toothed wheels (77, 79) adjacent to the rest of the stage (4), which can allow different rotation speeds between the two stages (2, 4). The support shaft (74) may be supported by stops and hydrodynamic bearings, directly integrated and lubricated in the driven pinion, which make the design lighter and more compact. The shaft (74) and the toothed wheels (77, 79) ingeniously transmit the loads from the stage (2) to the stage (4) in such a way as to cancel out the usual hydraulic loads, stemming from pressure, and mechanical, forces stemming from rotational drivings on the driven pinion (12).

A method of lubricating a coupling shaft of a gear pump includes communicating lubricant from a first gear stage along a first splined end section of the coupling shaft and through a first slot in a first radial shoulder of the coupling shaft, and also communicating lubricant from a second gear stage along a second splined end section of the coupling shaft and through a second slot in a second radial shoulder of the coupling shaft. The first radial shoulder is axially spaced from the second radial shoulder by an axial distance SA along an axis of rotation of the coupling shaft. The first and second slots each define a lowermost radial dimension SR from the axis of rotation, with a ratio SR/SA of 0.25-0.77.

A shaft assembly includes a shaft with a first radial shoulder and a second radial shoulder. The first radial shoulder and the second radial shoulder each include at least one slot. An axial separation between the first radial shoulder and the second radial shoulder defines an axial distance SA along an axis of rotation. The at least one slot defines a lowermost radial dimension SR from the axis of rotation. A ratio of SR/SA is 0.25-0.77.

A fuel system for an internal combustion engine includes a low pressure pump with a priming check valve. The priming check valve extends into the outlet flow path at a junction of the outlet flow path and a priming flow path that connects an inlet flow path of the low pressure pump to the outlet flow path.