Internal gear pump and internal gear motor

An internal gear pump comprising:

• an internal gear rotatably fitted in a body;
• an external gear inscribed in and meshed with the internal gear;
• a filler piece that partitions a liquid feeding space formed between the internal gear and the external gear into a high pressure region and a low pressure region;
• and
• a sealing member that covers both end surfaces of both the gears in a rotation axis direction and seals the liquid feeding space, wherein
• a plurality of communication grooves are formed, the plurality of communication grooves including a communication groove for communicating with an enclosed space surrounded by the filler piece and a tooth groove of at least one of the gears with the high pressure region, wherein each of the plurality of communication grooves ends in the high pressure region and has a respective start point that is configured to overlap with the enclosed space as both the gears rotate, and wherein the plurality of communication grooves are formed so that the high pressure region and the enclosed space communicate with each other at different timings as both the gears rotate,
• wherein the plurality of communication grooves include a plurality of outer communication grooves communicating with an outer enclosed space surrounded by the filler piece and the tooth grooves of the internal gears with the high pressure region, and a plurality of inner communication grooves communicating with an inner enclosed space surrounded by the filler piece and the tooth grooves of the external gear with the high pressure region, wherein each of the plurality of outer communication grooves is formed so that the high pressure region and the outer enclosed space communicate with each other at different timings as both the gears rotate, and each of the plurality of inner communication grooves is formed so that the high pressure region and the inner enclosed space communicate with each other at different timings as both the gears rotate, and
• the communication groove is formed such that a cross-sectional area communicating with the enclosed space continuously increases, wherein an increase rate of the cross-sectional area acceleratively increases as a rotation phase of both the gears advances.