TECHNICAL FIELD

The present invention relates to a one-way clutch having a plurality of cams between an inner race and an outer race and configured such that radially inner engagement surfaces and radially outer engagement surfaces of the cams frictionally engage an outer circumferential engagement surface of the inner race and an inner circumferential engagement surface of the outer race, respectively, when the inner race is rotated in one direction or when the outer race is rotated in the other direction, and such that the inner race or the outer race freewheels when the inner race is rotated in the other direction or when the outer race is rotated in one direction.

BACKGROUND ART

Existing one-way clutches used in applications where the inner race and outer race freewheel at high speed use a retainer that retains cams. The cams are retained by the retainer fixed to either the inner race or the outer race that freewheels at high speed to cause the cams to rotate in the same direction as the inner race or outer race so that a centrifugal force is applied to the cams to turn (lift off) the cams. This is to bring both the radially inner engagement surfaces and radially outer engagement surfaces of the cams out of contact with the outer circumferential surface of the inner race and/or the inner circumferential surface of the outer race so as to prevent wear on the radially inner and outer engagement surfaces of the cams.

Meanwhile, there have also been proposed other types of one-way clutches that transmit torque from the inner race or outer race to the cams when the inner race and outer race freewheel by way of a configuration other than the one that uses a retainer fixed to the inner race or outer race to transmit torque from the inner race or outer race to the cams. The following are examples of the one-way clutch described above.

CITATION LIST

Patent Literature

[Patent Literature 1] Japanese Patent Application Publication No. 2005-106135

[Patent Literature 2] Japanese Patent Application Publication No. 2007-092870

Patent Literature 1 discloses a one-way clutch that uses a wire cage connected to a pair of side plates, which are fixed to the outer race, for retaining the plurality of cams set between the inner race and the outer race in a circumferentially equally spaced manner. This way, torque can be transmitted from the outer race to the cams via the retainer fixed to the outer race.

Patent Literature 2 discloses a one-way clutch that uses an inner retainer and an outer retainer for retaining the plurality of cams set between the inner race and the outer race in a circumferentially equally spaced manner. The outer retainer is fixed to the outer race. The cams have a blade-like portion. According to this configuration, the blade-like portions of the cams receive a fluid such as lubricant or air when the outer race rotates to cause the cams to turn.

However, the one-way clutch having a retainer has following issues. Namely, issues such as an increase in the size of the one-way clutch because of the retainer, breakage of the retainer caused by collision between the retainer and the cams resulting from vibration or the like applied to the one-way clutch, and the difficulty and the cost of producing a retainer having a complex structure.

Another type of one-way clutch used for applications in which the inner race and outer race freewheel at low speed is not provided with a retainer. The cams in this case are restricted from moving axially and retained between the inner race and the outer race by side plates positioned on both sides in the axial direction of the cams. The side plates are not fixed to the inner race or the outer race. Therefore, when the inner race and outer race freewheel, the radially inner engagement surfaces and radially outer engagement surfaces of the cams slide on the outer circumferential engagement surface of the inner race and the inner circumferential engagement surface of the outer race. The one-way clutch with this configuration is affected to a limited extent by the wear on the radially inner engagement surfaces and radially outer engagement surfaces of the cams in cases where the inner race and outer race freewheel at low speed. However, this configuration is not suited to one-way clutches used in applications where the inner race and outer race freewheel at high speed, since the influence of wear on the radially inner engagement surfaces and radially outer engagement surfaces of the cams increases in cases where the inner race and outer race freewheel at high speed.

Another issue with some one-way clutches is biasing means provided to bias the plurality of cams either radially inward or outward, which also makes it difficult to reduce the axial size of the one-way clutch. Further problem is the large work burden due to the large number of components to be handled during the assembly of the clutch.

SUMMARY OF INVENTION

Technical Problem

Accordingly, in view of the issues in the existing techniques described above, an object of the present invention is to provide a one-way clutch that is simple and easy to manufacture, made smaller in an axial direction, lightweight and unbreakable, and capable of preventing wear on radially inner engagement surfaces and radially outer engagement surfaces of cams in periods of high-speed freewheeling.

Solution to Problem

The present invention solved the above issues by providing a one-way clutch including an inner race and an outer race rotatable relative to each other around an identical axis; and a plurality of cams provided in a circumferential direction between the inner race and the outer race, the plurality of cams each frictionally engaging the inner race and the outer race when the inner race is rotated in one direction or when the outer race is rotated in the other direction, and the plurality of cams each disengaging from the inner race and the outer race when the inner race is rotated in the other direction or when the outer race is rotated in one direction, wherein at least one of the inner race and the outer race includes side plates that rotate with the inner race or the outer race and positioned on both sides in an axial direction of the cams, and the plurality of cams are each configured to receive a predetermined centrifugal force to turn in an engaging direction in which the cams engage the inner race and outer race when the inner race and outer race rotate together in a same direction.

Advantageous Effects of Invention

According to the invention set forth in claim1, the plurality of cams provided between the outer race and the inner race are retained by side plates sandwiching them in the axial direction. The retainer is thus dispensed with in the present invention. The clutch is therefore unbreakable, simple-structured and easy to manufacture, as well as small and lightweight, since failures resulting from breakage of the retainer do not occur.

The plurality of cams are each configured to turn in an engaging (meshing) direction when they receive a centrifugal force. That is, the torque that is usually applied to the cams by biasing means such as springs is given by the centrifugal force that acts on the center of gravity of the cams when the cams rotate in the same direction as the outer race and inner race. The cam behaviors can be stabilized and power transmission performance can be achieved as designed according to the present invention even though there are no biasing means. The one-way clutch is thus made even smaller in the axial direction (thinner).

Furthermore, the reduction in the number of components lessens the burden of assembling work, which makes manufacturing of the one-way clutch easy.

According to the configuration set forth in claim2, the side plates are annular plates that cover a radially inner portion or a radially outer portion of each of the plurality of cams, and spaces between inner surfaces of the side plates and respective end faces of the plurality of cams are filled with lubricant. The plurality of cams are each configured to separate from an outer circumferential engagement surface of the inner race by viscosity of the lubricant when either the inner race or the outer race rotates in a direction in which the cams disengage. Thus the radially inner engagement surfaces of the cams are brought out of contact with the outer circumferential engagement surface of the inner race when the one-way clutch freewheels, so that wear on the radially inner engagement surfaces and radially outer engagement surfaces of the cams can be prevented in periods of high-speed freewheeling of the inner race or outer race.

According to the configuration set forth in claim3, the plurality of cams are aligned in contact with each other so that closed space is formed by circumferential surfaces of adjacent cams, an outer circumferential surface of the inner race, and inner surfaces of the radially inner side plates. As the lubricant is continually supplied into the closed space via an oil passage formed in the inner race during freewheeling of the one-way clutch, pressure is applied in a direction in which the volume of the closed space is increased, so that the respective radially inner engagement surfaces of the plurality of cams can be brought out of contact with the outer circumferential engagement surface of the inner race when the one-way clutch freewheels. Therefore, wear on the radially inner engagement surfaces and radially outer engagement surfaces of the cams can reliably be prevented in periods of high-speed freewheeling.

The plurality of cams being aligned circumferentially with little looseness can also realize a high transmittable torque capacity.

According to the configuration set forth in claim4, the state in which the radially inner engagement surfaces of the cams are not in contact with the outer circumferential engagement surface of the inner race can be reliably achieved by the action of the lubricant filling the spaces between the respective inner surfaces of the radially inner side plates and radially outer side plates and the respective end faces of the plurality of cams, in addition to the action of the pressure applied by the continuous supply of the lubricant during the freewheeling of the one-way clutch. Therefore, wear on the radially inner engagement surfaces and radially outer engagement surfaces of the cams can reliably be prevented in periods of high-speed freewheeling.

According to the configuration set forth in claim5, the retainer retains each of the plurality of cams in a circumferentially equally spaced manner. Therefore, each cam can turn without being restricted by adjacent cams, which allows speedy engagement or disengagement between all of the cams and the inner race and outer race, when the inner race or outer race is rotated.

