Abstract: A multiribbed power transmission belt and method of manufacturing the same, wherein an unvulcanized belt preform is provided with transversely extending staple fibers in the compression section thereof. The compression section is caused to be vulcanized while being urged against a mold having projections forming shallow grooves in the inner surface thereof. The grooves have a depth in the range of approximately 20% to 50% of the height of the ribs intended to be formed in the final power transmission belt. The ribs are formed in the belt by removing material from the compression section of the vulcanized preform, such as by the conventional machining operations of grinding, cutting, etc. The angular deflection of the reinforcing fibers in the compression section is caused to be no more than approximately 25% to provide the improved belt construction.

Abstract: A multiribbed power transmission belt having an inner portion of the compression section thereof defined by arcuate side surfaces converging inwardly. In one form, the side surfaces are circular. The outer portion of the compression section is defined by planar side surfaces converging inwardly. In one embodiment, the outer portion side surfaces are tangent to the inner portion arcuate surfaces and, in another form, the outer portion planar side surfaces intersect the arcuate side surfaces of the inner portion of the compression section. The distal tip of the ribs, in one form, is circular concentric with the side surfaces of the inner portion. In an alternative disclosed form, the tip surface is planar transversely to the rib.

Abstract: A timing belt having an outer section defined by cogged ribs defining a preselected controlled coefficient of friction obtained by providing controlled size grooves extending transversely through the ribs. The ratio of the effective side area of the grooves to the side area of the cogs defined in the ribs by the grooves, in the illustrated embodiment, is in the range of approximately 1/2 to 21/2 where the coefficient of the rib material is approximately 0.35. The cogs are raw edged and provided with a cover fabric. The provision of the cogged ribs permits the belt to be used as a double timing belt as well as providing improved functioning with backside rib pulleys. The effective coefficient of friction obtained by reducing the side area of the ribs as a result of the provision of the grooves is preferably in the range of 0.15 to approximately 0.90.