One-way clutch

Abstract: The present invention provides a one-way clutch (10) disposed in an annular space through which an outer ring (11) and an inner ring (12) face each other, the outer ring and the inner ring being disposed inside and outside each other in a diameter direction and concentrically with each other. A lubricant used for lubricating an inner peripheral face of the outer ring and an outer peripheral face of the inner ring on which rollers (13) roll is prepared by mixing a urea-based consistency increasing agent into ester-based or synthetic oil-based base oil with a pressure viscosity coefficient (at a temperature of 25°C) set at 12GPa -1 or more. By the lubricant, movements of state switching components are stabilized even at a low temperature and wear of the state switching components and operating faces can be suppressed even at a high temperature.

Description: Field of the Invention The present invention relates to a one-way clutch. The one-way clutch is used for a pulley of auxiliary machinery such as a feed mechanism for various equipment, an alternator for an automobile, and a compressor, a water pump, and a cooling fan for an air conditioner, for example. Description of the Related Art One-way clutches of the above kind are known, for example, from U.S.-A-3 426 874, which represents the closest state of the art. This document shows a self-energizing synchronizing clutch, wherein the synchronization is achieved by the use of rollers between an inner race splined to the main shaft and an outer race secured to the desired gear. The rollers are controlled by a shaft ring and shifting keys actuating an inner and an outer cage for the rollers. The inner race has cam surfaces thereon so that shifting of the inner and outer cages forces the rollers upon the cam surfaces of the inner race, and the rollers are wedged between the inner and outer races by the torque of the gear. Moreover, JP-09208982-A (see also patent abstracts of Japan, Volume 1997, No. 12, 25 December 1997) discloses a grease for encapsulating in a bearing which retains its high-temperature durability and its good lubricity over the wide temperature range from low to high temperatures so as to prevent developing allophone when it is cold. Some of the one-way clutches are of a type disposed between an outer ring and an inner ring which are disposed inside and outside each other in a diameter direction and concentrically with each other and having a clutch function of switching between a lock state in which the outer ring and the inner ring are rotated synchronously with each other and a free state in which the outer ring and the inner ring are rotated with respect to each other. Such one-way clutches include a type of clutch employing rollers for the above clutch function. The rollers of this type of one-way clutch are disposed in wedge-shaped spaces formed at some positions on a circumference of a space in a diameter direction and through which the inner and outer rings face each other. A gap of each the wedge-shaped space in the diameter direction narrows in one direction in a circumferential direction. Through the wedge-shaped spaces, cam faces of the outer ring and an outer peripheral face of the inner ring face each other, the cam faces having recessed curved faces which are recessed outward in the diameter direction and provided at some positions on a circumference of an inner peripheral face of the outer ring and the outer peripheral face of the inner ring being disposed on an inner side in the diameter direction. In the above one-way clutch, the lock state is obtained by rolling the rollers to narrower sides of the wedge-shaped spaces to engage the rollers with the cam faces of the outer ring and the outer peripheral face of the inner ring which are operating faces for the rollers and to integrate the outer ring with the inner ring. In this case, the engagement can be achieved by friction forces of the rollers against the operating faces. In such a one-way clutch, a lubricant is used to lubricate the rollers and the operating faces thereof in order to improve abrasion resistance. In this case, although the lubricant is effective at improving the abrasion resistance, an engaging property reduces and the switching operation of the one-way clutch becomes unstable if the lubrication works excessively in the lock state. By urea-based grease conventionally and commonly used as a lubricant, both the abrasion resistance and engaging property can be obtained in a relatively narrow range of temperature, but it is hard to obtain the both in a wide range of temperature from a low temperature to a high temperature. Specifically, the engaging property of the rollers is poor at the low temperature while the abrasion resistance is poor at the high temperature. The present inventor proposes to mount a one-way clutch to an alternator and to allow rotation of a rotor of the alternator to continue by an inertial force of the rotor when a rotation number of the crankshaft reduces, thereby improving power generation efficiency. According to such a structure, because vibration of the engine is transmitted almost all the time to a pulley of the alternator through a belt for driving the pulley for rotation, especially the abrasion resistance is likely to decrease. SUMMARY OF THE INVENTION Therefore, it is a main object of the present invention to provide a one-way clutch in which an operation of switching between lock and free states in a wide range of temperature from a low temperature to a high temperature is stable. It is another object of the invention to provide a one-way clutch in which both the engaging property and abrasion resistance can be obtained in the wide range of temperature. It is yet another object of the invention to provide a one-way clutch in which movement of rollers is stable even at a low temperature and abrasion resistance of the rollers and operating faces of the rollers is improved even at a high temperature. Other objects, features, and advantages of the invention will become apparent from the following descriptions. According to the invention, there is provided a one-way clutch according to clam 1. In the invention, because the ingredients of the used lubricant are selected, movement of the state switching component is stabilized even at the low temperature and the state switching component and the operating faces are less likely to wear even at the high temperature. Preferably, the state switching component is a roller disposed for rolling in a wedge-shaped space formed between an inner peripheral face of the outer ring and an outer peripheral face of the inner ring. In this case, the roller is less likely to slip when rolling against a narrower side of the wedge-shaped space. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects as well as advantages of the invention will become clear by the following description of preferred embodiments of the invention with reference to the accompanying drawings, wherein: FIG. 1 is a vertical sectional front view of a one-way clutch of an embodiment of the present invention; FIG. 2 is a plan developed view showing a portion of the one-way clutch in FIG. 1; FIG. 3 is a front view of the one-way clutch in FIG. 1; FIG. 4 is a vertical sectional side view of a pulley unit incorporating the one-way clutch of the above embodiment. In all these figures, like components are indicated by the same numerals. DETAILED DESCRIPTION OF THE INVENTION With reference to FIGs. 1 to 4, a one-way clutch according to a preferred embodiment of the present invention will be described in detail. A one-way clutch 10 has an outer ring 11, an inner ring 12 disposed inside the outer ring 11 in a diameter direction and concentrically with the outer ring 11, a plurality of rollers 13 disposed between an inner peripheral face of the outer ring 11 and an outer peripheral face of the inner ring 12, a cage 14 for retaining the respective rollers 13, and a plurality of coil springs 15 disposed to individually correspond to each roller 13 for biasing each corresponding roller 13 in one direction in a circumferential direction. The inner peripheral face of the outer ring 11 has a circular shape in section. The outer peripheral face of the inner ring 12 is formed with flat key-shaped cam faces 12a at equal intervals on a circumference, thereby appearing that the inner ring 12 has a polygonal shape in section. However, a cylindrical shape remains partially between the respective adjacent cam faces 12a in the circumferential direction. Consequently, a plurality of wedge-shaped spaces each narrowing in one direction in the circumferential direction are formed between the inner peripheral face of the outer ring 11 and the respective cam faces 12a of the inner ring 12, the inner peripheral face and the cam faces 12a facing each other. Each the roller 13 is disposed for rolling in both directions in the circumferential direction in each the wedge-shaped space. The cage 14 is fitted to an outside of the outer peripheral face of the inner ring 12 to contact the cylindrical portions remaining partially in the circumferential direction. The cage 14 has pockets 14a extending to open inside and outside in a diameter direction at areas corresponding to the respective cam faces 12a of the inner ring 12. Each roller 13 is individually housed by each pocket 14a. The cage 14 is fixed to the inner ring 12 by fitting of projecting portions 14b provided to one end in an axial direction into slit-shaped recessed portions 12b provided to the inner ring 12. The plurality of coil springs 15 are housed by and disposed within the respective pockets 14a of the cage 14 in a state in which each the coil spring 15 is compressed and adjacent to the roller 13 in the circumferential direction. Each coil spring 15 pushes each roller 13 in one direction in the circumferential direction, i.e., toward a narrower side of the wedge-shaped space by its extension restoring force. The coil spring 15 has a shape of an ellipse when seen from an end face in the circumferential direction so as to avoid skewing of the roller 13. Thus, the coil spring 15 contacts with as large area as possible thereof in an axial direction of the roller 13. Although, in the above one-way clutch 10, components (state switching components) for switching between a lock state and a free state as described later in description of operation are rollers 13, the components are not limited to the rollers 13. Operating portions of the roller 13 are the inner peripheral face of the outer ring 11 and the cam faces 12a of the inner ring 12, the inner peripheral face and the cam faces 12a facing the wedge-shaped space. Operation will be described below. First, in a case of usage in which the outer ring 11 is driven to rotate only in one direction to cause the inner ring 12 to follow, each the roller 13 is caused to roll toward the narrower side of the wedge-shaped space when a rotation speed of the outer ring 11 is increased. As a result, the rollers 13 are engaged between the outer ring 11 and the inner ring 12 and the inner ring 12 is integrated with the outer ring 11 and rotates synchronously with the outer ring 11. This state is referred to as the lock state. However, if a rotation speed of the inner ring 12 becomes higher than that of the outer ring 11 due to decrease in the rotation speed of the outer ring 11, the roller 13 is caused to roll toward a wider side of the wedge-shaped space against a spring force of the spring 15 and starts to rotate on its own axis and the outer ring 11 and the inner ring 12 rotate with respect to each other. This state is referred to as the free state. In a case of a usage in which the outer ring 11 is rotated arbitrarily in opposite directions, if the outer ring 11 rotates clockwise in FIG. 1, the clutch is brought into the above-described lock state in which the inner ring 12 rotates synchronously with the outer ring 11 in the same direction. If the outer ring 11 rotates counterclockwise in FIG. 1, the clutch is brought into the above-described free state in which rotation power is not transmitted from the outer ring 11 to the inner ring 12, only the outer ring 11 rotates, and the inner ring 12 does not rotate. For the one-way clutch 10, a lubricant prepared by mixing urea-based consistency increasing agent into ester-based or synthetic oil-based base oil, for example, is used. Five to 20 % by weight, and preferably 10 to 15 % by weight of the urea-based consistency increasing agent is added. In addition, antioxidant, rust preventive, extreme pressure agent, and the like are added properly. As the base oil of the lubricant, one with a pressure viscosity coefficient of 12GPa -1 or more (preferably 16GPa -1 or more) at a temperature of 25°C is selected. A ratio of the base oil and the consistency increasing agent mixed to prepare the lubricant is set such that a consistency is in a range of 240 to 310 (preferably 270 to 290) at a temperature of 25°C and a traction coefficient is 0.02 or more (preferably 0.04 or more) at a temperature of 25°C. An engaging property and abrasion resistance of the one-way clutch 10 when various lubricants are used are evaluated by the following experiment. In this experiment, eight lubricants in total including Examples 1 to 4 shown in table 1 and Comparative Examples 1 to 4 shown in table 2 were prepared. For the lubricants of Examples 1 to 4, the pressure viscosity coefficient of the base oil (at the temperature of 25°C) was fixed at 12GPa -1 or more, the consistency of the lubricants (at the temperature of 25°C) was fixed at 240 to 310, and the traction coefficient of the lubricants (at the temperature of 25°C) was fixed at 0.02 or more. For the lubricants of Comparative Examples 1 to 4, the base oil and the consistency increasing agent specified in the invention were used. For the lubricant of Comparative Example 1, the consistency and the traction coefficient are set at values out of the range of the invention. For the lubricant of Comparative Example 2, the pressure viscosity coefficient and the consistency were set at values out of the range of the invention. For the lubricant of Comparative Example 3, the traction coefficient was set at a value out of the range of the invention. For the lubricant of Comparative Example 4, the pressure viscosity coefficient was set at a value out of the range of the invention. Example number 1 2 3 4 Base oil ester synthetic oil synthetic oil synthetic oil consistency increasing agent urea ← ← ← Base oil viscosity 40°C 32 65 98 70 100°C 6 8 12 22 Pressure viscosity coefficient of the base oil 17.0 64.4 18.8 12.2 Consistency 276 283 240 310 Traction coefficient 0.044 0.056 0.023 0.066 Performance evaluation Engaging property Δ ○ × Δ Abrasion resistance ○ × Δ Δ Comparative Example number 1 2 3 4 Base oil synthetic oil ← ← ← Consistency increasing agent urea ← ← ← Base oil viscosity 40°C 40 378 80 33 100°C 8 88 25 7 Pressure viscosity coefficient of the base oil 14.5 4.0 13.0 10.9 Consistency 236 330 244 293 Traction coefficient 0.018 0.070 0.018 0.028 Performance evaluation Engaging property Δ ○ × Δ Abrasion resistance ○ × Δ Δ In the performance evaluation in the above tables, the engaging property was evaluated by checking a following state of rotation of the inner ring 12 with respect to rotation of the outer ring 11 in the lock state and in a low-temperature atmosphere (at -20°C to -40°C). The abrasion resistance was evaluated by checking wearing states of the cam faces 12a of the inner ring 12 and an inner peripheral face of the outer ring 11 after operation in a high-temperature atmosphere (at 100°C to 120°C). With regard to the engaging property, a mark ○ represents a case in which the rotation of the inner ring 12 stably followed the rotation of the outer ring 11, a mark Δ represents an unstable case in which the rotation of the inner ring 12 did not follow the rotation of the outer ring 11 frequently, and a mark × represents a case in which the rotation of the inner ring 12 did not follow the rotation of the outer ring 11. With regard to the abrasion resistance, a mark ○ represents a case in which wear was hardly found, a mark Δ represents a case in which wear was found, and a mark × represents a case in which wear was extremely significant. The result was that the engaging operation of the rollers 13 was smooth for a long time and significant wear was not generated in the rollers 13 and the cam faces 12a when the lubricants of Examples 1 to 4 were employed. In contrast to the examples, the engaging property decreased slightly in the case of the lubricant of Comparative Example 1, the abrasion resistance decreased significantly in the case of the lubricant of Comparative Example 2, and the engaging property decreased significantly in the case of the lubricant of Comparative Example 3. Both the engaging property and the abrasion resistance decreased slightly in the case of the lubricant of Comparative Example 4. The above results indicate that pressure resistance tends to increase to suppress generation of breakage of oil film if the pressure viscosity coefficient of the base oil (at the temperature of 25°C) is set at 12GPa -1 or more. If the consistency (at the temperature of 25°C) is set at 240 to 310, flowability tends to increase to enhance wearing suppression effect. If the traction coefficient (at the temperature of 25°C) is set at 0.02 or more, the rollers 13 is less likely to slip and the engaging property is excellent. In the above-described one-way clutch 10, movement of the rollers 13 is stable even at a low temperature and the rollers 13 and members to which the rollers 13 contact (the cam faces 12a of the inner ring 12 and the inner peripheral face of the outer ring 11) are less likely to wear even at a high temperature, which contributes to enhancement of reliability and increase in life of the clutch. The one-way clutch 10 can be built into pulleys of various auxiliary machinery mounted to an engine of an automobile and the like, for example. A specific example in which the one-way clutch 10 is incorporated into the pulley of an alternator as auxiliary machinery of the automobile is shown in FIG. 4. FIG. 4 is a vertical sectional side view of a pulley unit incorporating the one-way clutch. In FIG. 4, a reference character A indicates a whole pulley unit, a reference numeral 1 indicates a pulley, 2 indicates a rotary shaft, and 3, 3 indicate rolling bearings. The pulley 1 is formed at an outer peripheral face thereof with a belt groove 1a in which a driving belt B is rove. The rotary shaft 2 functions as an input shaft of the alternator. The rolling bearings 3, 3 are disposed on opposite sides in an axial direction in an annular space through which the pulley 1 and the rotary shaft 2 face each other and mainly bear a radial load. Both the rolling bearings 3, 3, are formed as deep groove ball bearings. In the pulley unit A in the example shown in FIG. 4, seal members 5 are mounted to only outer end sides of the two rolling bearings 3, 3 in an axial direction between the inner and outer rings. By the two seal members 5, the one-way clutch 10 and the rolling bearings 3, 3 are sealed and a common lubricant is used for the one-way clutch 10 and the two rolling bearings 3, 3. In the pulley unit A in the example shown in FIG. 4, the one-way clutch 10 is disposed in the annular space through which the pulley 1 and the rotary shaft 2 face each other. In this example, the outer ring 11 of the one-way clutch 10 is fitted into the pulley 1 by press-fit and the inner ring 12 of the one-way clutch 10 is fitted into the rotary shaft 2 by press-fit. Such a pulley unit A is used in a state in which the pulley 1 is rotated in only one direction and a rotation speed of the pulley 1 is changed arbitrarily. The operation is similar to that of the one-way clutch 10 described above. In other words, if the pulley 1 is rotated in a required direction by the belt B, the one-way clutch 10 is brought into the lock state as the rotation speed increases to transmit rotation power from the pulley 1 to the inner ring 12 and the rotary shaft 2 substantially at a rate of 1 to 1. However, if the rotation speed of the pulley 1 decreases temporarily in an increasing process of the rotation speed of the pulley 1, the rotation speeds of the inner ring 12 and the rotary shaft 2 momentarily increase over the rotation speed of the pulley 1 due to rotational inertial forces. As a result, the one-way clutch 10 is brought into the free state to interrupt transmission of the rotation power from the pulley 1 to the rotary shaft 2. Then, if the rotation speed of the pulley 1 exceeds the rotation speed of the rotary shaft 2 again, the one-way clutch 10 is again brought into the lock state, and as a result, the rotation power is transmitted from the pulley 1 to the rotary shaft 2. As described above, even if the rotation speed of the pulley 1 increases and decreases (pulsation), the one-way clutch 10 is properly switched between the lock state and the free state to rectify the pulsation of the rotation speed of the pulley 1, thereby linearly transmitting the rotation to the rotary shaft 2. Also when the rotation speed of the pulley 1 is decreased, the one-way clutch 10 is brought into the free state to allow the rotary shaft 2 to be rotated at a high speed by the rotational inertial force of the rotary shaft 2 itself. Therefore, it is possible to improve power generation efficiency of the alternator. Although the above pulley unit A frequently receives vibration from an engine, the above-described specific lubricant is used for the one-way clutch 10, and therefore, the operation of the one-way clutch 10 is stabilized and the abrasion resistance of the one-way clutch 10 is enhanced for a long time, which contributes to enhancement of reliability and increase in life of the pulley unit A. In the one-way clutch 10, the state switching component may be constructed of a sprag or other components instead of the rollers 13. Leaf springs or elastic chips may be used instead of the coil springs 15. Although the cam faces 12a of the one-way clutch 10 are formed on the inner ring 12 side in the above embodiment, the present invention can be also applied to the one-way clutch 10 in which the cam faces 12a are formed on the outer ring 11 side. However, because the structure in which the cam faces 12a are formed on the inner ring 12 like in the above embodiment can prevent the rollers 13 from being detached unnecessarily from the locked positions due to a centrifugal force even in high-speed rotation, such a structure is suitable for usage in the high-speed rotation.

Claims: A one-way clutch (10) comprising: an outer ring (11); an inner ring (12) disposed inside said outer ring (11) in a diameter direction and concentrically with said outer ring (11); a plurality of locking members (13,15) being disposed between the outer ring (11) and the inner ring (12) for switching between a lock state in which said outer ring (11) and said inner ring (12) are rotated synchronously with each other and a free state in which said outer ring (11) and said inner ring (12) are rotated with respect to each other; and a lubricant for lubricating an operating portion of said locking member (13,15) and a space between the outer ring (11) and the inner ring (12), characterized in that the one-way clutch (10) further comprises a rolling bearing (3), and sealing members (5) sealing said locking member (13,15), said rolling bearing (3) and said lubricant, wherein said lubricant lubricates said locking member (13,15) and said rolling bearing (3) commonly, said lubricant being prepared by mixing a urea-based consistency increasing agent into ester-based or synthetic oil-based base oil, the base oil having a pressure viscosity coefficient, at a temperature of 25° C, set at 12 GPa -1 or more. The one-way clutch according to claim 1, wherein said outer ring (11) and said inner ring (12) are disposed such that a wedge-shaped space narrowing in one direction in a circumferential direction is formed between faces of said outer ring (11) and said inner ring (12) which face each other and said state locking member (13,15) is disposed for rolling in said wedge-shaped space.

Inventors: FUJIWARA HIDEKI, NAKAGAWA YOSHITAKA, TAZUMI HAJIME, TERADA TADAHIRO, FUJIWARA, HIDEKI, NAKAGAWA, YOSHITAKA, TAZUMI, HAJIME, TERADA, TADAHIRO, Fujiwara, Hideki, c/o Koyo Seiko Co., Ltd., Nakagawa, Yoshitaka, c/o Koyo Seiko Co., Ltd., Tazumi, Hajime, c/o Koyo Seiko Co., Ltd., Terada, Tadahiro, c/o Koyo Seiko Co., Ltd.
Applicants: KOYO SEIKO CO, KOYO SEIKO CO., LTD.
Application year: 2000
Main classification: F16D41
IPC codes: F16D41, C10M169