Abstract: A gear pump constructed in such a manner that bearing bushings are pressedly inserted in bushing insertion holes for supporting gear shafts therein, side plate are arranged on both sides of gears, and a part of hydraulic oil in a suction chamber is circulated through a lubricating oil introduction passage formed on an inside of each of the bearing bushings and a lubricating oil return passage formed on an outside of each of the bearing bushings. The lubricating oil return passages have outlets positioned in a manner to be laterally symmetric on the basis of a vertical line defined by connecting centers of the gear shafts and vertically symmetric on the basis of a horizontal line extending through a center of the vertical line and perpendicular to the vertical line. The side plates each are formed with a through-hole which is positioned on one side of the vertical line so as to be communicated to both outlets of the lubricating return passages vertically symmetric on the basis of the horizontal line.

Abstract: In order to prevent a decrease in volumetric efficiency from occurring when a gear pump or motor, 10, is operated at room temperature after operating at a lower temperature or when it is operated at a higher temperature after operation at a lower temperature, the housing, 13, containing two interlocking gears 17 and 18 is made of a ferrous material, which is the same as that of the two gears, and a large number of serrated grooves, 40, are disposed in the axial direction on the low pressure side of the inner wall surfaces of the gear bower 16.

Abstract: A seal mechanism in gear pumps or motors, in which a pair of gears engage, so that at least one side surface of these gears is sealed by a pressure plate movable in the direction of the shaft, the said pressure plate is partitioned by a seal member in the shape of a figure "3" at the back into the low pressure zone and the high pressure zone which lead to the inlet side pressure and the outlet side pressure, respectively, both ends of the said seal member are formed in a loop-like shape, and block members for backup use, movable with respect to the pressure plate, are housed in the loop-like parts, so that the said block members may be pressed toward the low pressure side through the seal member by the liquid pressure which is connected to the high pressure zone during the operation of the gear pump or motor, so that these block members may press the end parts of the seal member to the inner wall surface of the gear bower in the housing and so that no liquid may leak from these parts.

Abstract: At least one pair of intermeshing impeller gears are supported by bearings such as bushings or roller bearings. Liquid drawn through the suction port is forced first to flow perpendicular to the axes of the gears toward one ends of the shafts or trunions thereof and then through a low pressure passage extended in parallel with the axes of the gears and communicated with the pump chamber in opposed relationship with the zone where the teeth of the gears are disengaging. Each bearing is formed with a lubrication or oil groove or passage. One port or end remote from the side face of the gear of the lubrication or oil groove is communicated with the low pressure passage at the closed end thereof or at a position adjacent to the inlet thereof through a passage while the other port or end is communicated through a passage with the low pressure passage at a position between the inlet and closed end thereof.

Abstract: A gear pump or motor wherein at least two pump or gear units are arranged in coaxial relationship and have their axially inwardly extended driven and driving shafts journalled in a common intermediate casing, the driving shafts being splined together with an internally splined sleeve. The inlet port opened in the intermediate casing is communicated through low-pressure passages with the pump chambers of the respective pump or motor units (and with the assembly chamber or pocket formed to accommodate the opposing ends of the axially inwardly extended driving shafts). The diameter of the inlet port is made larger than the size of the sleeve for interconnecting the driving shafts so that the sleeve may be inserted through the inlet opening into the assembly chamber or pocket and interconnect the driving shafts. Thus, in assembly the interconnection between the driving shafts may be much facilitated.

Abstract: A gear pump is disclosed wherein the shafts of at least a pair of intermeshing gears are rotatably supported in bushings each with an axially extended lubrication groove formed in the bore of the bushing, one end of the lubrication groove being communicated through a low pressure chamber defined in the inner end face of the bushing with a portion of a suction port located adjacent to the root or dedendum circle of the gear while the other end of the lubrication groove being communicated with the suction port through a hole extended through the bushing or casing or notch formed therein, whereby part of the liquid drawn through the suction port upon rotation of the intermeshing gears is forced into the pressure chamber because of the fact that the liquid drawn into each tooth space of the gear is imparted with the impact speed directed in the radial direction of the tooth space due to the difference between the speed with which the liquid is drawn into the gear pump and the rotational speed of the intermeshing

Abstract: Disclosed is a pressure loaded gear pump wherein two assemblies each consisting of a pair of abutted bushings are axially slidably fitted into a casing on both sides of a pair of intermeshing impeller gears for supporting rotatably the shafts thereof and for sealing the side faces of the gears; and defined on each side of the casing between the pair of abutted bushings and an end plate are a low pressure chamber into which is admitted the hydraulic pressure in a suction opening, a high pressure chamber into which is admitted the hydraulic pressure in a discharge opening and two moderate pressure chambers each of which is communicated with a sector between the suction opening and the pressure transition or gradient sector of the liquid passage from the suction to discharge openings. The effective area of each moderate pressure chamber is equal to or slightly greater than the cross sectional area of the space between the teeth of the gears.