COUPLING DEVICE FOR POWER TRANSFER

Abstract: A coupling device for power transfer between drive and driven shafts (25, 26) coaxially arranged with each other for relative rotation, which includes an inner member (11) mounted on one end of the drive shaft (25) for rotation therewith and having an eccentric cylindrical support portion (11a) the central axis (A) of which is radially displaced from the central axis (B) of the drive shaft, an outer cylindrical casing (12) coaxially connected to one end of the driven shaft (26) for rotation therewith and being arranged in surrounding relationship with the support portion (11a) of the inner member, the casing having a number of internal teeth (12b) formed therein, and an inscribed gear (13) rotatably carried by the support portion (11a) of the inner member and being in meshing engagement with the internal teeth (12b) of the casing to transfer the power only from the drive shaft (25) to the driven shaft (26) in response to the difference in rotational speed between the shafts, and a separator rotatably carried by the support portion of the inner member and having a guide portion disposed between a portion of the external teeth and a portion of the internal teeth to maintain the meshing engagement of the external teeth with the internal teeth at their other portions.

Description: The present invention relates to a coupling device for power transfer between drive and driven shafts coaxially arranged with each other for relative rotation, and more particularly to a coupling device for transmitting the power from the drive shaft to the driven shaft in response to the difference in rotational speed between the shafts. In Japanese Utility Model Early Publication No. 59-188731, there is disclosed a viscous coupling device wherein an amount of high viscous fluid is stored to effect power transfer between drive and driven shafts when it has been sheared due to the difference in rotational speed between of the shafts. Disclosed in Japanese Patent Early Publication No. 63-240429 is a viscous coupling device which includes a friction clutch for effecting power transfer between drive and driven shafts when it has been engaged. The friction clutch is arranged to be engaged by a pressure of high viscous fluid applied thereto in response to the difference in rotational speed between the shafts. In such conventional viscous coupling devices, the power is transmitted from the drive shaft to the driven shaft and vice versa. In application to the drive system of a four-wheel drive vehicle, however, it is required to prevent transfer of the drive torque from the driven shaft to the drive shaft. DE-960,772 discloses a one-way clutch providing a coupling between a pair of coaxial shafts capable of relative rotation. An eccentric inner member is provided on one shaft and is disposed within a cylindrical outer casing provided on the other shaft. An intermediate pressure member is located eccentrically on the inner member to drivingly engage the outer member, with a compression spring being provided to maintain this engagement. The clutch is engaged when the inner and outer members rotate relative to one another in one direction and disengaged when they rotate in the opposite relative direction. It is, therefore, an object of the present invention to provide a coupling device capable of transmitting the power only from the drive shaft to the driven shaft in response to the difference in rotational speed between the shafts and of preventing transfer of the drive torque from the driven shaft to the drive shaft. Another object of the present invention is to provide a coupling device suitable for use in the drive system of a four-wheel drive vehicle as a differential, a differential locking mechanism or a limited-slip differential. According to the present invention, the objects are attained by providing a coupling device for power transfer between drive and driven shafts coaxially arranged with each other for relative rotation, which is in accordance with Claim 1. In a practical embodiment of the present invention, it is preferable that the cylindrical casing is formed therein with a number of internal teeth, the intermediate rotary member is in the form of an inscribed gear formed thereon with a number of external teeth in meshing engagement with the internal teeth of the casing, and the means for maintaining the engagement of the rotary member with the internal surface of the casing is in the form of a separator having an annular flange rotatably carried by the eccentric cylindrical support portion of the inner member and a guide portion of semi-circular cross-section extending perpendicularly from an outer periphery of the annular flange and disposed between a portion of the external teeth and a portion of the internal teeth to maintain the meshing engagement of the external teeth with the internal teeth at their other portions. For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawing, in which: Fig. 1 is a sectional view of a coupling device in accordacne with the present invention; Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1; and Fig. 3 is a schematic illustration of the drive system of a four-wheel drive vehicle equipped with the coupling device shown in Figs. 1 and 2. Referring now to the drawings, Fig. 1 illustrates a preferred embodiment of a coupling device 10 in accordance with the present invention. As shown in Fig. 3, the coupling device 10 is disposed in the rear-wheel drive system of a four-wheel drive vehicle which is equipped with a transaxle 22 including a power transmission assembled with a prime engine 21 and a transfer device united with the power transmission. The transfer device is arranged to transfer the power from prime engine 21 to a set of front road wheels 24, 24 through a pair of split axle shafts 23, 23 and to a front propeller shaft 25 drivingly connected to a rear propeller shaft 26 by means of the coupling device 10. The rear propeller shaft 26 is drivingly connected to a rear differential 27 which acts to transmit the power from propeller shaft 26 to a set of rear road wheels 29, 29 through a pair of split axle shafts 28, 28. As shown in Figs. 1 and 2, the coupling device 10 includes, as main component parts, an inner shaft 11, an outer cylindrical casing 12, an inscribed gear 13 and a separator 14. The inner shaft 11 has an eccentric cylindrical support portion 11a of large diameter, an internally splined bore 11b, and a sleeve portion 11c of small diameter. The eccentric cylindrical support portion 11a of shaft 11 has a central axis A radially displaced from the center of internally splined bore 11b. The inner shaft 11 is mounted on an externally splined rear end 25a of the front propeller shaft 25 for rotation therewith in such a manner that the central axis A of eccentric cylindrical support portion 11a is radially displaced from the central axis B of propeller shaft 25. The outer cylindrical casing 12 has a closed end 12c connected to a front end of the rear propeller shaft 26 for rotation therewith and an open end 12a which is closed by a cover member 15 in a fluid-tight manner. The rear end 25a of front propeller shaft 25 is rotatably carried by the closed end 12c of casing 12 through a ball bearing, and the cover member 15 is rotatably supported on the sleeve portion 11c of inner shaft 11 through a needle bearing in a fluid-tight manner. The outer cylindrical casing 12 is formed therein with a number of internal teeth 12b which are arranged in surrounding relationship with the eccentric cylindrical support portion 11a of inner shaft 11. The inscribed gear 13 is formed thereon with a number of external teeth 13a the outer diameter of which is smaller than the inner diameter of casing 12. The inscribed gear 13 is rotatably carried by the eccentric cylindrical support portion 11a of inner shaft 11 and is positioned in an axial direction by means of a pair of axially spaced snap rings 16a, 16b through an annular flange 14a of separator 14. As shown in Fig. 2, the separator 14 has a guide portion 14b of semi-circular cross-section extending perpendicularly from an outer periphery of annular flange 14a and is rotatably supported on the cylindrical support portion 11a of inner shaft 11 at its annular flange 14a. The annular flange 14a of separator 14 is positioned in an axial direction by means of the snap rings 16a, 16b through the inscribed gear 13, and the guide portion 14b of separator 14 is disposed between the internal teeth 12 of casing 12 and the external teeth 13a of inscribed gear 13. In this arrangement, the guide portion 14b of separator 14 is in contact with a portion of the external teeth 13a at its inner surface so that the other portion of external teeth 13a is maintained in meshing engagement with a portion of the internal teeth 12b of casing 12. In operation, the inner shaft 11 rotates about the central axis B of front propeller shaft 25 when applied with the power from the prime engine 21 through the transaxle 22 and front propeller shaft 25. The rotation of inner shaft 11 causes the inscribed gear 13 to rotate with the eccentric cylindrical support portion 11a of inner shaft 11. Thus, the outer cylindrical casing 12 is driven by rotation of the inscribed gear 13 in meshing engagement therewith to rotate the rear propeller shaft 26, and in turn, the rear differential 27 is driven by rotation of the rear propeller shaft 26 to drive the rear road wheels 29, 29 through split axle shafts 28, 28 for four-wheel drive. Assuming that the rear propeller shaft 26 has been driven by a drive torque applied thereto from the rear road wheels 29 through rear differential 27 during travel of the vehicle, the rotational speed of rear propeller shaft 26 becomes higher than that of front propeller shaft 25. In this instance, relative rotation of the cylindrical casing 12 to the front propeller shaft 25 causes the inscribed gear 13 to freely rotate about the cylindrical support portion 11a of inner shaft 11. Thus, the coupling device 10 acts to prevent transfer of the drive torque from the rear propeller shaft 26 to the front propeller shaft 25. From the above description, it will be understood that the coupling device 10 can be assembled in a simple manner and constructed small in size. In the coupling device 10, the external teeth 13a of inscribed gear 13 is maintained in meshing engagement with the internal teeth 12b of casing 12 to transfer the power from the front propeller shaft 25 to the rear propeller shaft 26. This is effective to eliminate the occurrence of high heat in the coupling device 10 and to ensure the power transfer from the front propeller shaft 25 to the rear propeller shaft 26 without causing undesired influences to the driving performance of the vehicle. Although a certain specific embodiment of the present invention has been shown and described, it is obvious that many modifications and variations thereof are possible in light of these teachings. For example, the internal teeth 12b of casing 12 may be eliminated for frictional engagement with an intermediate rotary member substituted for the inscribed gear 13.

Claims: A coupling device for power transfer between drive and driven shafts (25,26) coaxially arranged with each other for relative rotation, comprising: an inner member ( 11 ) mounted on one end of the drive shaft (25) for rotation therewith and having an eccentric cylindrical support portion (11a) the central axis (8) of which is radially displaced from the central axis (B) of the drive shaft; an outer cylindrical casing (12) coaxially connected to one end of the driven shaft (26) for rotation therewith and arranged in surrounding relationship with the eccentric cylindrical support portion (11a) of said inner member (11); and, an intermediate rotary member (13) freely rotatably carried by the eccentric cylindrical support portion (11a) of said inner member (11) and being drivingly engaged with an internal surface of said cylindrical casing (12); characterized in that said intermediate rotary member (13) is arranged concentrically with said inner member (11); and, means (14) are provided for permanently maintaining the engagement of said rotary member (13) with the internal surface of said casing (12). A coupling device as claimed in Claim 1, wherein said cylindrical casing (12) is formed therein with a number of internal teeth (12b), and said intermediate rotary member (13) is an inscribed gear formed thereon with a number of external teeth (13a) in meshing engagement with the internal teeth (12b) of said casing (12). A coupling device as claimed in Claim 2, wherein said means for permanently maintaining the engagement of said rotary member with the internal surface of said casing is a separator (14) having an annular flange (14a) rotatably carried by the eccentric cylindrical support portion (11a) of said inner member (11) and a guide portion (14b) of semi-circular cross-section extending perpendicularly from an outer periphery of said annular flange (14a) and disposed between a portion of said external teeth (13a) and a portion of said internal teeth (12b) to permanently maintain the meshing engagement of said external teeth (13a) with said internal teeth (12b) at their other portions.

Inventors: INUI, MASAKI C/O TOYOTA JIDOSHA KABUSHIKI KAISHA
Applicants: TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1989
Main classification: F16D41
IPC codes: F16H1, F16D43, F16D41, B60K17, F16D1