TECHNICAL FIELD

The present disclosure relates to a reduction gear equipped with a detection device that detects the state of a rolling bearing provided on an output shaft.

BACKGROUND ART

As a reduction gear for a kneader extruder that kneads and extrudes a resin, rubber, and the like, a two-speed switching reduction gear described in Patent Document 1, for example, is known. The rotation speed of the rotor of the kneader extruder is switched between high-speed condition and low-speed condition by the two-speed switching reduction gear, and thus the throughput, kneading temperature, and kneading quality of a kneaded product are adjusted.

The two-speed switching reduction gear includes an input shaft having an outer-circumferential face to which a low-speed side pinion and a high-speed side pinion are fixed, an output shaft that is disposed in parallel with the input shaft, and a rotation speed switching mechanism. On the output shaft, a low-speed side gear that engages with the low-speed side pinion and a high-speed side gear that engages with the high-speed side pinion are each idlably mounted through a bearing. The rotation speed switching mechanism selectively links the low-speed side gear and the high-speed side gear with the output shaft.

In the case in which the low-speed side gear is linked with the output shaft, the rotation (power) of the input shaft is transmitted to the output shaft through the low-speed side pinion and the low-speed side gear, and as a result, the output shaft rotates at low speed. On the other hand, in the case in which the high-speed side gear is linked with the output shaft, the rotation (power) of the input shaft is transmitted to the output shaft through the high-speed side pinion and the high-speed side gear, and as a result, the output shaft rotates at high speed. Note that in both cases, in the low-speed side gear and the high-speed side gear, the gear that is not linked with the output shaft idles about the rotating output shaft at a rotation speed different from the rotation speed of the output shaft.

CITATION LIST

Patent Document

Patent Document 1: JP 2010-159826 A

SUMMARY OF THE INVENTION

Here, the bearing between the low-speed side gear and the output shaft and the bearing between the high-speed side gear and the output shaft are both rotate integrally with the output shaft and the gears in the transmission of power. Thus, no relative velocity is produced between an inner ring and an outer ring that constitute the bearing. Since no relative velocity is produced between the inner ring and the outer ring, a rolling element of the bearing keeps in contact with the inner ring and the outer ring at the same places in the state in which a load is applied. To these contact places, mechanical vibrations are applied, and damage that is referred to as fretting corrosion (surface damage (wear) that occurs due to relative micro motion repeatedly acting on two contacting surfaces in a periodic manner) is produced and developed in a lapse of time.

As the abnormality diagnosis of a bearing, it is known that generally, vibrations of the bearing housing (the inner ring and the outer ring) are measured, vibrations at a frequency (a bearing damage frequency) due to an inner ring scratch or an outer ring scratch are monitored, and thus the presence or absence of an abnormality in the bearing is determined.

However, in the two-speed switching reduction gear having a structure as described in Patent Document 1, since the bearing is located in the inside of the gear (the low-speed side gear and the high-speed side gear), it is difficult to measure vibrations of the bearing. Since the inner ring and the outer ring of the bearing do not relatively rotate in the transmission of power, no bearing damage frequency for use in abnormality determination appears, and thus the above-described general abnormality diagnosis method for a bearing is not applicable. Therefore, in order to diagnose an abnormality in a bearing, it has been desired to establish a bearing state detection method that is different from conventional methods.

The present disclosure has been made in view of the circumstances. An object is to provide a reduction gear equipped with a bearing state detection device that can detect the state of a rolling bearing rotating integrally with an output shaft and an output gear in the transmission of power.

The reduction gear includes a casing, an input shaft that is rotatably supported on the casing, at least one input gear that is fixed to the input shaft, and that rotates together with the input shaft, an output shaft that is rotatably supported on the casing such that the output shaft is disposed in parallel with the input shaft, at least one rolling bearing including an inner ring that is fixed to the output shaft and an outer ring that is relatively rotatable to the inner ring, at least one output gear that is fixed to the outer ring of the at least one rolling bearing and that engages with the at least one input gear, a linking mechanism that is switchable between a linking state in which the at least one rolling bearing is bypassed such that the at least one output gear and the output shaft integrally rotate and the at least one output gear is linked with the output shaft and a releasing state in which a link between the at least one output gear and the output shaft is released, and a detection device that detects a state of the at least one rolling bearing. The at least one input gear includes an input-gear outer circumferential part on which helical threads are formed, the at least one output gear includes an output-gear outer circumferential part on which helical threads that engage with the helical threads of the input-gear outer circumferential part are formed, and an output-gear side surface that is orthogonal to an axial direction of the output shaft, and the detection device includes a plurality of displacement sensors that are opposed to the output-gear side surface of the at least one output gear at a position at a predetermined distance from a rotation axis of the output shaft in a radial direction, and that detect a displacement of the output-gear side surface in the axial direction, and a processing unit that acquires a tilt amount to the rotation axis of the output-gear side surface based on the displacements of the output-gear side surface detected by the plurality of displacement sensors in rotation of the output gear which is linked with the output shaft by the linking mechanism, and that detects a state of the rolling bearing from the tilt amount.

