Frictional piece

A friction part for a frictionally operating device, comprising:

• a friction lining carrier;
• and
• a friction lining comprising a plurality of friction lining pieces arranged on the friction lining carrier to form an annular friction surface;
• wherein the friction lining pieces are each arranged in a first row comprising same friction lining pieces and a second row comprising same friction lining pieces;
• wherein the annular friction surface comprises:
• an inner edge;
• an outer edge;
• and
• a groove set formed between the plurality of friction lining pieces, the groove set comprising:
• a first stem groove extending from the inner edge to a first branching point between the inner edge and the outer edge;
• a first branch groove extending from the first branching point to a first connecting point between the inner edge and the outer edge;
• a second branch groove extending from the first branching point to a second connecting point between the inner edge and the outer edge;
• a third branch groove extending from a second branching point between the inner edge and the outer edge to the second connecting point;
• and
• a second stem groove extending from the second connecting point to the outer edge;
• wherein the first stem groove, the first branch groove, and the second branch groove are arranged in a y shape;
• wherein the second stem groove, the second branch groove, and the third branch groove are arranged in an inverted y shape;
• wherein the first stem groove or the second stem groove comprises a first groove width;
• the first branch groove, the second branch groove, or the third branch groove comprises a second groove width;
• and
• a ratio of the first groove width to the second groove width is greater than 0.5 and less than 6;
• wherein a first proportion of the annular friction surface comprising the groove set is on average substantially constant over a diameter of the annular friction surface in a radially inner region of the annular friction surface and in a radially outer region of the annular friction surface,
• wherein the annular friction surface comprises a radially central region between the radially inner region and the radially outer region;
• and
• a second proportion of the annular friction surface comprising the groove set varies over the diameter in the radially central region;
• wherein the radially inner region comprises 30-70% of a radial dimension R of the annular friction surface,
• the radially inner region extends at a minimum 50% of the radial dimension R;
• and
• the radially central region extends at a maximum 85% of the radial dimension R.