Continuously variable toroidal transmission

Abstract: The toroidal continuous variable transmission has a viscous clutch(25, 25A) installed between the output disks(3,5) to allow their rotation difference even when there is a difference in the transmission ratio between the two toroidal speed change units(6, 7). If the transmission ratio difference increases, the viscous clutch(25, 25A) causes the two units(6, 7) to synchronize with each other, thus preventing the two speed change units(6, 7) from remaining unequal in the transmission ratio. Further, when the transmission ratio difference between the two toroidal speed change units(6 , 7) is small, the toroidal continuous variable transmission has a function to self-synchronize the two units(6, 7). When the transmission ratio difference becomes large, the differential mechanism(22) is activated to prevent seizure due to interlocking or slippage. With this toroidal speed change unit(6, 7), when an electrical failure occurs, it is possible to fix the transmission ratio to a predetermined value on the low-speed side according to the driver's selection of gearshift position so as to ensure safe driving while running with a heavy load on a descending slope by preventing sudden application of engine braking while traveling at high speed.

Description: The present invention relates to a toroidal continuous variable transmission used in automobiles and more particularly to a toroidal continuous variable transmission which has two toroidal speed change units arranged on the same axis, each comprising oppositely arranged input and output disks, power rollers rotating in contact with the input and output disks to transmit the input disk rotation to the output disk while continuously changing the speed of the input disk rotation according to a tilt angle of the power rollers, and trunnions supported on the power rollers. The toroidal continuous variable transmission generally has a toroidal speed change unit, which comprises an input disk, an output disk and power rollers disposed between the both disks and which transfers the rotation power of the input disk driven by an input shaft to the output disk through the power rollers, with the rotation power further transmitted from the output disk to an output shaft. For improved transmitting capacity and efficiency, a layout has been developed whereby two toroidal speed change units are mounted on the same axis. A conventional toroidal continuous variable transmission, as shown in Figure 5, has two toroidal speed change units 43, 47, which comprise input disks 40, 44, output disks 41, 45 and tiltable power rollers 42, 46 that transmit torque (see Japan Patent Laid-Open No. 174034/1994, for example). This toroidal continuous variable transmission is of a double cavity type in which two toroidal speed change units 43, 47 are mounted opposite each other on the input shaft 48. The input disk 40 is supported on the input shaft 48 so that it is rotatable reactive to the input shaft. It can also be securely coupled to the input shaft 48 by a loading cam 49 so that it rotates together with the input shaft 48. The other input disk 44 is secured to the input shaft 48 so that it rotates together with the input shaft 48. The input shaft 48 is supported axially movable slightly with respect to a casing not shown. The output disks 41, 45 are disposed opposite the input disks 40, 44 and supported rotatable relative to the input shaft 48. The output disks 41, 45 are connected to each other through a hollow shaft 50. The hollow shaft 50 has secured thereto an output gear 51, which is in mesh with a gear 53 of an output shaft 52. The power rollers 42 are disposed between the input disk 40 and the output disk 41 and have frictional engagement with the toroidal surfaces of the both disks 40, 41. The power rollers 46 are disposed between the input disk 44 and the output disk 45 and are in frictional engagement with the toroidal surfaces of the both disks 44, 45. The power rollers 42, 46 are rotatable about their own rotation axes 54, 55 and tiltable about tilt axes 56, 57 perpendicular to the rotation axes 54, 55. The toroidal continuous variable transmission has a link mechanism to cause the power rollers 42, 46 to tilt in synchronism with each other so that their tilt angles are equal. As the tilt angle of the power rollers 42, 46 changes, the frictional contact points between the power rollers 42, 46 and the input disks 40, 44 and output disks 41, 45 change, thus effecting continuous speed change. The rotation power transmitted from the input disks 40, 44 to the output disks 41, 45 through the power rollers 42, 46 is transmitted by the shearing force of oil under high pressure, i.e., traction force (viscous frictional force). To obtain a desired traction force requires a very large pressing force at the contact point between the power rollers 42, 46 and the both disks. This pressing force is produced by pressing the input disk 40 against the output disk 41 by the loading cam 49. Another example of conventional toroidal continuous variable transmission is shown in Figure 6 (see Japan Patent Laid-Open No. 174034/1994, for example). This toroidal continuous variable transmission is of a double cavity type, in which two toroidal speed change units 66, 67 are mounted opposite each other on the same axis and comprise input disks 62, 64, output disks 63, 65 and power rollers 68, 69 that tilt about tilt axes 71 perpendicular to rotation axes 70 and couple the input and output disks. The construction of the toroidal speed change units 66, 67 is the same as that of the toroidal speed change units 43, 47. The conventional speed change units of Figure 5 have the output disks 41, 45 directly coupled together, whereas the second conventional example of Figure 6 couples the output disks 63, 65 through a differential mechanism 82. The differential mechanism 82 comprises: side gears 73, 75 connected to the output disks 63, 65 through hollow shafts 72, 74; pinions 76 meshed with the side gears 73, 75; a differential case 78 having pinion shafts 77 rotatably supporting the pinions 76; and an output gear 79 secured to the differential case 78 and meshed with a gear 81 of an output shaft 80. In the toroidal continuous variable transmission of Figure 6, when the output disks 63, 65 are rotating at the same revolution speed, the side gear 73 connected to one of the output disks 63 and the side gear 75 connected to the other output disk 65 rotate at the same speed. Hence, the pinions 76 in mesh with the side gears 73, 75 do not rotate on their own pinion shafts 77 but revolve around the input shaft 61. When the transmission ratios of the toroidal speed change units 66, 67 differ, however, the revolution speeds of the output disks 63, 65 differ, so that one of the side gears rotates at higher speed than the other. As a result, the pinions 76 in mesh with both of the side gears 73, 75 spin on their own axes while revolve around the input shaft 61. In the conventional transmission of Figure 5, the transmission ratios of the two toroidal speed change units 43, 47 may not always be equal due to differences in the units' response at the time of speed change operation. When the disagreement in the transmission ratio is within a very small range, the toroidal speed change unit with a greater transmission ratio performs the speed change operation to reduce the transmission ratio and the other unit with a smaller transmission ratio performs to increase the transmission ratio so that the two units synchronize with each other. However, as the difference in the transmission ratio becomes large, the conventional transmission of Figure 5 is interlocked before self-synchronization is achieved, leading to a very dangerous situation. For example, consider a case where the transmission ratio of one toroidal speed change unit is higher than, or on the speed-increase side of, that of the other toroidal speed change unit. Because the pair of input disks are coupled together in the rotation direction on the input shaft, they rotate at the same speed and one of the output disks in the unit with a higher transmission ratio tends to rotate at a higher speed than the other output disk. However, because the pair of output disks are also coupled together on the output shaft, they are only allowed to rotate at the same revolution speed. That is, both the input shaft and the output shaft are locked and cannot perform an intended rotating action. This is analogous to a situation where 2-speed gear and 3-speed gear in the manual transmission engage at the same time. In this way, as the transmission ratio difference increases, both the input shaft and the output shaft of the transmission cannot rotate before self-synchronization is achieved, resulting in a transmission lockup. If the transmission does not lock, the contact portion between the power rollers and the both disks in the toroidal speed change unit, i.e., the traction contact portion, slips and may get seized by the heat produced. On the contrary, in the second conventional transmission shown in Figure 6, because the pair of output disks are coupled through the differential mechanism 82, if there is any discrepancy in the transmission ratio between the two toroidal speed change units, the revolution difference between the pair of output disks is absorbed by the differential mechanism 82 in the form of pinion rotation on its own axis. Hence, when a difference occurs between the transmission ratios of the two toroidal speed change units, it is possible to prevent a slip at the traction contact portion. It should be noted, however, that the transmission ratio difference between the two toroidal speed change units, if occurred, is normally very small and that in a region of a very small transmission ratio difference, the slip at the traction contact portion poses no problem. In spite of this fact, with the above conventional transmission, the differential function is activated at all times regardless of the magnitude of the transmission ratio difference, inactivating the self-synchronization function. Hence, the overall transmission efficiency of the toroidal continuous variable transmission decreases to that extent. A toroidal continuous variable transmission disclosed in Japan Patent Laid-Open No. 174034/1994 has an input shaft, a pair of input disks that rotate with the input shaft, a pair of output disks disposed opposite the corresponding input disks and supported on the input shaft so that they are rotatable relative to the input shaft, tiltable power rollers disposed between the opposing input disks to the output disks, a differential mechanism that couples the output disks, and an output shaft connected to the differential mechanism. The differential mechanism may be a bevel gear type differential mechanism or a planetary gear type differential mechanism. In this toroidal continuous variable transmission, because the two output disks are coupled through the differential mechanism, if a discrepancy occurs between the transmission ratios of the two toroidal speed change units, the difference in the revolution speed of the two output disks is absorbed by the differential mechanism. Hence, no slip occurs at the traction contact portions in the toroidal speed change units. But the self-synchronization function fails to work, giving rise to a possibility of the transmission ratios of the two units remaining unequal. JP-A-62-258255 discloses a toroidal continuous variable transmission having the features of the pre-characterising portion of claim 1. JP-A-6-174034 discloses the features of the precharacterising portion of claim 5. The present invention provides a toroidal continuous variable transmission having: an input shaft; a pair of input disks that rotate with the input shaft; a pair of output disks disposed opposite the corresponding input disks and rotatably mounted on the input shaft; tiltable power rollers disposed between the opposing input disks and output disks to transfer torque from the input disks to the output disks; and an output shaft; characterised in that a viscous clutch is provided on the output side of the output disks which can allow a rotation difference smaller than a predetermined amount between the output disks and which can prevent a rotation difference between the output disks from exceeding the predetermined amount; and the output shaft is connected to the viscous clutch. In this toroidal continuous variable transmission, because the two output disks of the first toroidal speed change unit and the second toroidal speed change unit are drivably connected to the output shaft through the viscous clutch, the torque from the output disks is transmitted from the input-side disk of the viscous clutch to the output-side disk and out to the output shaft through the output gear. Even when there is a difference in the transmission ratio which is smaller than a predetermined amount, between the first and second toroidal speed change units, the input portion of the viscous clutch, capable of allowing relative rotation between the engagement members, can absorb rotation difference between the output disks and transmit power, thus eliminating interlock of the transmission equipment and preventing excessively large inputs from being applied to the toroidal speed change unit, which in turn prevents slippage of the contact portions between the power rollers and the disks. If the transmission ratio difference between the first and the second toroidal speed change units becomes large and when the rotation difference is greater than a predetermined amount, the viscous clutch locks the both output disks, forcibly synchronizing the two toroidal speed change units. This self-synchronization function prevents an unwanted situation where the torques are not transmitted rendering the car unable to run. For example, when the first toroidal speed change unit is deviated toward the speed-increase side beyond the second toroidal speed change unit, the viscous clutch increases the load of the first toroidal speed change unit as in the conventional transmission equipment, shifting the first unit toward the speed-decrease side. Conversely, when the first toroidal speed change unit is deviated toward the speed-decrease side beyond the second toroidal speed change unit, the viscous clutch reduces the load of the second unit shifting it toward the speed-increase side. In this way, the first and second toroidal speed change units maintain the self-synchronization function. A differential mechanism is preferably installed between the two output disks. This mechanism can be a bevel gear type differential mechanism, which comprises a pair of side gears drivably connected to the output disks, pinions meshed with the both side gears, a differential case rotatably supporting the pinions, and an output gear secured to the differential case and drivably connected to the output shaft. Alternatively, the differential mechanism may be a planetary gear type differential mechanism. Because the two output disks are coupled through the differential mechanism, the difference in the transmission ratio between the two toroidal speed change units, if it occurs, can be absorbed by the differential mechanism of bevel gear type or planetary gear type, without reducing the overall efficiency of the equipment as a whole or producing heat at the traction contact portion. When a difference occurs in the power roller tilt angle between the two toroidal speed change units due to deformation of power roller supporting members, the transmission ratio difference between the units cannot be absorbed with the conventional toroidal continuous variable transmission. With the toroidal continuous variable transmission of this invention, however, this difference can be absorbed. This toroidal continuous variable transmission obviates the need for strictly synchronizing the power rollers' tilt angles of the two toroidal speed change units, as is required with the conventional equipment, and offers the advantage of being able to simplify the speed change control of the two speed change units. With the conventional toroidal continuous variable transmission, it is necessary to apply a large pressing force at all times by the loading cam in order to prevent slippage between the power rollers and the input/output disks and thereby stabilize the operation. This results in the overall equipment size becoming large. With the toroidal continuous variable transmission of this invention, however, because no slippage or heat is produced at the traction contact portions, there is no need to apply a large pressing force, which in turn contributes to reducing the equipment size. The present invention also provides a toroidal continuous variable transmission having: an input shaft; a pair of input disks that rotate with the input shaft; a pair of output disks disposed opposite the corresponding input disks and rotatably mounted on the input shaft; tiltable power rollers disposed between the opposing input disks and output disks to transfer torque from the input disks to the output disks; a differential mechanism to drivably connect the output disks and an output shaft; characterised in that a clutch transmits and interrupts torque between the output disk; and the output shaft is drivably connected to the differential mechanism. The differential mechanism may comprise a pair of side gears, pinions meshed with the both side gears, a differential case rotatably supporting the pinions, and an output gear secured to the differential case and drivably connected to the output shaft, and wherein the clutch transmits and interrupts torques between a pair of engagement members, with one engagement member connected to one of the side gears and to one of the output disks and with the other engagement member connected to the other side gear and the other output disk. Alternately, the differential mechanism may be a planetary gear mechanism, which comprises a sun gear connected to one of the output disks, pinions connected to the other output disk and meshed with the sun gear, a carrier supporting the pinions, and a ring gear meshed with the pinions and drivably connected to the output shaft, and wherein the clutch transmits and interrupts torques between a pair of engagement members, with one engagement member connected to the sun gear and with the other engagement member connected to the carrier. When a planetary gear mechanism is adopted as the differential mechanism, it is preferred that a double pinion type planetary gear mechanism be used which comprises a first pinion in mesh with the sun gear and a second pinion in mesh with the ring gear and the first pinion. The clutch may be a clutch, an electromagnetic clutch, a slip joint or a torque limiter, or any other type that allows relative rotation between the input and output shafts. As mentioned above, because this toroidal continuous variable transmission couples the pair of output disks through the differential mechanism, the transmission equipment assumes the same state as that of the conventional transmission equipment shown in Figure 5 when the clutch is engaged and, when it is disengaged, assumes the same state as that of the conventional equipment shown in Figure 6. When the difference in transmission ratio between the two toroidal speed change units is small, the clutch is engaged. As a result, the two toroidal speed change units synchronize with each other until the transmission ratios of the two units are equal. When the transmission ratio difference between the units becomes large, the clutch is disengaged. Because the rotation difference between the paired output disks is absorbed by the differential mechanism, it is possible to prevent slippage at the traction contact portions in the toroidal speed change units. In this toroidal continuous variable transmission, when a transmission ratio difference occurs between the two toroidal speed change units but is small, the self-synchronization function is activated to synchronize the transmission ratios of the two toroidal speed change units, limiting the reduction in the transmission efficiency of the transmission equipment as a whole. When the transmission ratio difference is large, it is absorbed by the differential mechanism, preventing the equipment from being interlocked or the traction The preferred embodiments of the present invention can provide a double cavity type toroidal continuous variable transmission with a self-synchronization function, which, when a difference produced in the transmission ratio between the two toroidal speed change units is smaller than a predetermined amount, allows the rotation difference between the two output disks thereby preventing seizure due to interlocking and slippage in the transmission equipment and, when the transmission ratio difference exceeds the predetermined amount, forcibly synchronizes the two units by the viscous clutch thus preventing the two units from remaining unequal in the transmission ratio. The preferred embodiments of the present invention can also provide a toroidal continuous variable transmission, which, when the transmission ratio difference between the two toroidal speed change units is small, maintains the self-synchronization function and, when the difference becomes large, activates the differential mechanism to prevent seizure due to interlocking and slippage. Preferred embodiments of the present invention will now be described hereinbelow by way of example only with reference to the accompanying drawings, in which: Figure 1 is a schematic cross section showing the construction of the toroidal continuous variable transmission as one embodiment of this invention; Figure 2 is a schematic cross section showing the construction of the toroidal continuous variable transmission as another embodiment of this invention; Figure 3 is a schematic cross section showing the construction of the toroidal continuous variable transmission as a further embodiment of this invention; Figure 4 is a schematic cross section showing the construction of the toroidal continuous variable transmission as a further embodiment of this invention; Figure 5 is a schematic cross section showing the construction of one conventional toroidal continuous variable transmission; and Figure 6 is a schematic cross section showing the construction of another conventional toroidal continuous variable transmission. Now, a first embodiment of the toroidal continuous variable transmission according to this invention is described by referring to Figure 1. As shown in the figure, the toroidal continuous variable transmission is of a double cavity type in which two toroidal speed change units 6 and 7 are mounted opposite each other on the same input shaft 1, with a viscous clutch 25 provided on the output side of the toroidal speed change units 6, 7. The toroidal speed change unit 6 comprises an input disk 2, an output disk 3 disposed opposite the input disk 2, and power rollers 8 disposed between the input disk 2 and the output disk 3 and kept in frictional contact with the toroidal surfaces of the both disks. The toroidal speed change unit 7, like the toroidal speed change unit 6, includes an input disk 4, an output disk 5 and power rollers 9. The toroidal speed change units 6, 7 are provided with two power rollers each. The power rollers 8 and the power rollers 9 are rotatable on their own rotation axes 10 and tiltable about tilt axes 11 perpendicular to the rotation axes 10. The input shaft 1 is rotatably supported on the casing and receives torques from engine through a torque converter. The input disk 2, though rotatably mounted on the input shaft 1, can be coupled to the input shaft 1 through a loading cam (see reference number 49 in Figure 5) so that it can rotate with the input shaft 1. The output disk 3 arranged opposite the input disk 2 is supported on the input shaft 1 so that it is rotatable relative to the input shaft 1. The input disk 4, also rotatably supported on the input shaft 1, can be coupled to the input shaft 1 through another loading cam so that it can rotate with it. The output disk 5 disposed opposite the input disk 4 is rotatably supported on the input shaft 1. Between the output disks 3, 5 and an output shaft 20 is provided the viscous clutch 25, whose disks 23a, 23b on the input side are connected to hollow shafts 12, 14 on the output side of the output disks 3, 5 and whose disk 24 on the output side is connected to an output gear 19. The output gear 19 is in mesh with a gear 21 mounted on the output shaft 20. The viscous clutch 25 has a function of allowing for a rotation difference of less than a predetermined magnitude between the output disks 3, 5 and, for the rotation difference greater than the predetermined magnitude, fixing the output disks 3, 5. Next, the operation of the first embodiment of the toroidal continuous variable transmission is explained. As the input shaft 1 receives torque from the engine, the torque is transmitted through the loading cam to the input disk 2. At the same time, the torque is also transmitted through another loading cam from the input shaft 1 to the input disk 4. When the torque is transferred to the input disk 2, the input disk 2 rotates turning the power rollers 8, which in turn causes the output disk 3 to rotate. The torque transmitted to the input disk 4 is further conveyed to the output disk 5 through the power rollers 9. While the torque is being transmitted, when the power rollers 8, 9 are synchronously tilted through the same angle about the tilt axes 11, the frictional engagement points between the power rollers 8, 9 and the input and output disks 3, 5 change, thus performing the continuous speed change operation. The rotation of the output disk 3 is conveyed to the input-side disk 23a of the viscous clutch 25 and the rotation of the output disk 5 to the input-side disk 23b of the viscous clutch 25. When the transmission ratios of the toroidal speed change units 6, 7 are equal under normal running condition, or when the rotation difference between the output disks 3, 5 is below the predetermined value, the revolution speeds of the outputs disks 3, 5 are equal or have a difference within an allowable range, so that the viscous clutch 25 allows the relative rotation of these output disk while transmitting power. As a result, an output of the output disks 3, 5 balanced through the viscous clutch 25 is transmitted to the output shaft 20 through the output gear 19 and gear 21. This action prevents the transmission from being locked or a slip between the power rollers and the disks from occurring. When a difference greater than the predetermined magnitude occurs between the revolution speeds of the output disks 3, 5, the viscous clutch 25 couples the output disks 3, 5 causing them to rotate together, with the result that their output is conveyed to the output shaft 20 through the output gear 19 and gear 21. Hence, the toroidal speed change units 6, 7 are forcibly synchronized by the viscous clutch 25 causing the outputs of the output disks 3, 5 to be transferred through the output gear 19 and gear 21 to the output shaft 20. Next, by referring to Figure 2, a second embodiment of the toroidal continuous variable transmission according to this invention is explained. The second embodiment has the same construction as the first embodiment, except that the second embodiment has a differential mechanism 22. So, components identical with those of the first embodiment are given like reference numerals and their explanations are not repeated. This toroidal continuous variable transmission has a differential mechanism 22 installed between the output disks 3, 5 and the output shaft 20. The bevel gear type differential mechanism 22 comprises a side gear 13 connected to the output disk 3, a side gear 15 connected to the output disk 5 through a viscous clutch 25A, a pair of pinions 16 in mesh with the both side gears 13, 15, and an output gear 19 secured to a differential case 18 rotatably supporting the pinions 16 and also drivably connected to an output shaft 20. The output side of the output disk 3 is secured with one end of a hollow shaft 12 sleeved over the input shaft 1. The other end of the hollow shaft 12 is secured with the side gear 13 and with an inner disk 23 of the viscous clutch 25A. The output side of the output disk 5 is secured with one end of a hollow shaft 14 sleeved over the input shaft 1. The other end of the hollow shaft 14 is secured with an outer disk 24 of the viscous clutch 25A and with a side gear 15. The paired pinions 16 are disposed opposite each other with the input shaft 1 therebetween and are in mesh with both the side gears 13, 15. The pinions 16 are rotatably supported on pinion shafts 17 provided to the differential case 18, which is rotatably supported on the input shaft 1. The end surface of the differential case 18 is secured with the output gear 19. The output shaft 20 is arranged parallel to the input shaft 1, and a gear 21 secured to the output shaft 20 is meshed with the output gear 19. Next, the operation of the toroidal continuous variable transmission shown in Figure 2 is explained. As the input shaft 1 receives torque from the engine, the torque is transferred through the loading cam to the input disk 2. similarly, the torque is also transferred through the loading cam from the input shaft 1 to the input disk 4. When the torque is transferred to the input disk 2, the input disk 2 rotates, turning the power rollers 8, whose rotation is transmitted to the output disk 3. The torque transferred to the input disk 4 is conveyed to the output disk 5 through the power rollers 9. While the torque is transmitted, the synchronous tilting of the power rollers 8, 9 through the same angle about the tilt axes 11 causes the frictional engagement points between the power rollers 8, 9 and the input disks 2, 4 and output disks 3, 5 to change, thus performing the continuous speed change operation. The rotation of the output disk 3 is transmitted to the side gear 13 and the rotation of the output disk 5 to the side gear 15. When under the normal running state the transmission ratios of the toroidal speed change units 6, 7 are equal, the revolution speeds of the output disks 3, 5 are equal and the both side gears 13, 15 rotate at the same revolution speeds. Hence, the pinions 16 do not rotate on their axes but revolve around the input shaft 1. The revolution of the pinions 16 causes the differential case 18 and therefore the output gear 19 secured to the differential case 18 to rotate with the pinions 16. The rotation of the output gear 19 is transferred to the output shaft 20 through the gear 21 meshed with the output gear 19. When the transmission ratios of the toroidal speed change units 6, 7 become unequal due to, for instance, distortion of the input shaft 1 or deformation of the supporting members for the power rollers, a difference occurs between the rotation speeds of the output disks 3, 5. When, for example, the revolution speed of the output disk 3 becomes higher than that of the output disk 5, the side gear 13 connected to the output disk 3 rotates faster than the side gear 15 connected to the output disk 5. As a result, the pinions 16 spin on their own axes to absorb the rotation difference between the side gears 13, 15 while at the same time revolving around the input shaft 1. Therefore, because of the action of the differential mechanism 22 provided between the output disks 3, 5, even when the transmission ratios of the toroidal speed change units 6, 7 do not agree, no slip occurs at the traction contact portions in the toroidal speed change units 6, 7. Next, a third embodiment of the toroidal continuous variable transmission according to this invention is explained. This embodiment, though not shown, has the similar construction and function to the second embodiment with the differential mechanism 22, except for the construction of the differential mechanism. The third embodiment employs a double-pinion planetary gear type differential mechanism as the differential mechanism 22. In this embodiment, the differential mechanism includes a sun gear connected to the output disk 3, a carrier that supports pinions drivably connected to the output disk 5 and meshed with the sun gear, and a ring gear meshed with the pinions and connected to the output shaft 20. The ring gear is secured with the output gear 19, which is in mesh with the gear 21 of the output shaft 20. The operation of the third embodiment is similar to that of the second embodiment. Next, by referring to Figure 3, a fourth embodiment of the toroidal continuous variable transmission is explained. In the figure, this toroidal continuous variable transmission is of a double cavity type in which two toroidal speed change units 6, 7 are mounted opposite each other on the same axis. The toroidal speed change units 6, 7 have the similar constructions to those of the preceding embodiments. So, the identical members are given like reference numerals and their explanations are not repeated. In the fourth embodiment, there are provided a differential mechanism 112 and a clutch 113 between the output disks 3, 5 and an output shaft 139. The differential mechanism 112 is formed as a bevel gear type differential mechanism 112, which comprises a pair of side gears 114, 115, a pair of pinions 116 in mesh with the both side gears 114, 115, a differential case 117 rotatably supporting the pinions 116, and an output gear 118 secured to the differential case 117 and connected to the output shaft 139. The clutch 113 is a multiple disc friction clutch, which couples or decouples a pair of engagement members, i.e., friction members 119, 120 equipped with a number of friction discs, for transfer or interruption of torque. The friction member 119 is connected to the output disk 5 and the side gear 115, and the friction member 120 is connected to the output disk 3 and the side gear 114. The back of the output disk 3 is secured with one end of a hollow shaft 121 sleeved over the input shaft 1. The intermediate portion of the hollow shaft 121 is rigidly fitted with the side gear 114 and the other end of the hollow shaft 121 is rigidly connected with the friction member 120 of the clutch 113. The back of the output disk 5 is secured with one end of a hollow shaft 122 sleeved over the input shaft 1. The other end of the hollow shaft 122 is connected with one end of the friction member 119 of the clutch 113, the other end of which is rigidly connected with the side gear 115. The pair of pinions 116 are arranged opposite each other with the input shaft 1 therebetween and are in mesh with the both side gears 114, 115. The pinions 116 are also rotatably supported on pinion shafts 123 provided to the differential case 117, which in turn in rotatably supported on the input shaft 1. The end surface of the differential case 117 is rigidly fitted with the output gear 118. The output shaft 139 is arranged parallel to the input shaft 1, and the gear 124 fixed on the output shaft 139 is in mesh with the output gear 118. The clutch 113 is of a type that imparts the coupling force to the pair of friction members 119, 120 by a spring 125. The clutch 113 maintains a predetermined torque transmission capacity by the setting load of the spring 125 and the friction coefficient of the friction surface of the friction members 119, 120. When the difference between the transmission ratios of the two toroidal speed change units 6, 7 is small, the differential operation, as in the conventional equipment, is not allowed by the coupling force of the clutch 113, causing the units to self-synchronize with each other. When on the other hand the transmission ratio difference is large, i.e., when the torque received by the clutch 113 exceeds the torque transmission capacity of the clutch, the differential operation is allowed as when a viscous clutch is used but the differential limit force is constant because it depends on the torque transmission capacity of the clutch 113. Next, the operation of the fourth embodiment of the toroidal continuous variable transmission is described. When the input shaft 1 receives torque from the engine, the torque is transmitted through the loading cam to the input disk 2. At the same time, the torque is also transferred through the loading cam from the input shaft 1 to the input disk 4. When the torque is transmitted to the input disk 2, the input disk 2 rotates, turning the power rollers 8, whose rotation is transmitted to the output disk 3. The torque transferred to the input disk 4 is conveyed to the output disk 5 through the power rollers 9. While the torque is transmitted, the synchronous tilting of the power rollers 8, 9 through the same angle about the tilt axes 11 causes the frictional engagement points between the power rollers 8, 9 and the input disks 2, 4 and output disks 3, 5 to change, thus executing the continuous speed change operation. The clutch 113 has the friction members 119, 120 tightly coupled together by the force of the spring 125. These friction members remain coupled until a torque greater than the torque transmission capacity of the clutch 113 is received. In this state, when the pair of output disks 3, 5 are rotating at the same speed, i.e., the transmission ratios of the two toroidal speed change units 6, 7 are equal, the side gear 115 drivably connected to the output disk 5 and the side gear 114 connected to the output disk 3 rotate at the same speed. Hence, the pinions 116 meshed with the side gears 114, 115 revolve around the input shaft 1 without rotating on their own axes. Let us consider a case where a difference occurs between the transmission ratios of the two toroidal speed change units 6, 7. When the transmission ratio difference is small, the clutch 113 is strongly engaged by the force of the spring 125, so that the differentiation between the output disks 3, 5 is prohibited, resulting in the same self-synchronization as performed in the conventional equipment of Figure 7. In this case, there is no slip in the clutch nor any reduction in the transmission efficiency of the toroidal continuous variable transmission. When the transmission ratio difference between the two toroidal speed change units 6, 7 increases, the differential torque becomes large. When the differential torque exceeds the torque transmission capacity of the clutch 113, the clutch 113 starts slipping. For example, when the revolution speed of the output disk 3 becomes higher than that of the output disk 5, the side gear 114 rotates faster than the side gear 115. As a result, the pinions 116 meshed with the both side gears 114, 115 rotate on their own axes to absorb the revolution speed difference between the side gears 114, 115 while at the same time revolving around the input shaft 1. Hence, the transmission is prevented from being locked and no slip occurs at the contact points between the power rollers 8, 9 and the input disks 2, 4 and output disks 3, 5 in the toroidal speed change units 6, 7. Next, by referring to Figure 4 a fifth embodiment of the toroidal continuous variable transmission according to this invention is explained. A differential mechanism 126 is formed of a planetary gear mechanism, which includes a sun gear 127 connected to the output disk 5, a carrier 130 that supports pinions 128 connected to the output disk 3 and meshed with the sun gear 127 and pinions 129 in mesh with the pinions 128, and a ring gear 131 in mesh with the pinions 129 and drivably connected to the output shaft 139. A clutch 132 is a multiple disc type friction clutch, which couples or decouples a pair of engagement members―a friction member 133 and a friction member 134―for transfer or interruption of torque. The friction member 133 is connected with the output disk 5 and the friction member 134 with the carrier 130. The back of the output disk 3 is securely fitted with one end of a hollow shaft 135 sleeved over the input shaft 1. The other end of the hollow shaft 135 is rigidly connected with the carrier 130. The back of the output disk 5 is securely fitted with one end of a hollow shaft 136 sleeved over the input shaft 1. The other end of the hollow shaft 136 is securely connected with the sun gear 127. The central portion of the hollow shaft 136 is connected with the friction member 133 of the clutch 132. The ring gear 131 is rigidly fitted with an output gear 137, which is meshed with a gear 124 fixed to one end of the output shaft 139 arranged parallel to the input shaft 1. Next, the operation of the fifth embodiment is explained. The rotation of the output disk 3 is transferred to the carrier 130. The rotation of the output disk 5 is transferred to the sun gear 127. In the normal state, i.e., when the transmission ratios of the two toroidal speed change units 6, 7 are equal, the revolution speeds of the outputs disk 3 and the output disk 5 are the same, so that the pinions 128, 129 do not rotate on their axes, causing the sun gear 127, pinions 128, 129, carrier 130, ring gear 131 and output gear 137 to revolve around the input shaft 1 as one piece. The rotation of the output gear 137 is transferred to the output shaft 139 through the gear 124 meshed with the output gear 137. When there is a difference between the transmission ratios of the two toroidal speed change units 6, 7 due, for instance, to distortion of the input shaft 1 and deformation of the supporting members of the power rollers 8, 9, the output disks 3, 5 tend to rotate at different speeds. When the transmission ratio difference is small, the differential torque is also small, so that the clutch 132 remains tightly engaged causing the carrier 130 connected to the output disk 3 and the sun gear 127 connected to the output disk 5 to rotate together. In this way, when the transmission ratio difference, if it occurs, between the two toroidal speed change units 6, 7 is small, there is no difference in the revolution speed between the output disks 3, 5, so that the units self-synchronize with each other to make the transmission ratios equal. When the transmission ratio difference increases, the differential torque exceeds the torque transmission capacity of the clutch 132, causing the clutch 132 to slip, producing a difference in the revolution speed between the output disks 3, 5. When, for example, the revolution speed of the output disk 5 is higher than that of the output disk 3, the sun gear 127 connected to the output disk 5 rotates faster than the carrier 130 connected to the output disk 3. As a result, the pinions 128 rotate on their axes causing the meshing pinions 129 to rotate on their axes to absorb the rotation difference between the output disks 3, 5. Hence, even when the transmission ratios of the toroidal speed change units 6, 7 do not match, the differential mechanism 126 provided between the output disks prevents the traction contact portions in the toroidal speed change units 6, 7 from slipping. In the fifth embodiment, the engagement force of the clutch 132 is preset to a predetermined value by a spring 138 so that the differential operation is only allowed when the differential torque supplied to the toroidal continuous variable transmission exceeds the predetermined value. The clutch may be controlled so as to increase the engagement force when the transmission ratio difference is small and, when it becomes large, weaken the engagement force. In that case, a variety of control methods may be employed. One such control may involve electrically detecting the transmission ratios of the two toroidal speed change units, calculating their difference by a controller, and controlling the engagement force as by the hydraulic or electromagnetic force according to the calculated difference.

Claims: A toroidal continuous variable transmission having: an input shaft (1); a pair of input disks (2,4) that rotate with the input shaft (1); a pair of output disks (3,5) disposed opposite the corresponding input disks (2,4) and rotatably mounted on the input shaft (1); tiltable power rollers (8,9) disposed between the opposing input disks (2,4) and output disks (3,5) to transfer torque from the input disks (2,4) to the output disks (3,5); and an output shaft (2); characterised in that a viscous clutch (25;25A) is provided on the output side of the output disks (3,5) which can allow a rotation difference smaller than a predetermined amount between the output disks (3,5) and which can prevent a rotation difference between the output disks (3,5) from exceeding the predetermined amount; and the output shaft (20) is connected to the viscous clutch (25;25A). A toroidal continuous variable transmission according to claim 1, wherein a differential mechanism (22) is installed between the output disks (3,5). A toroidal continuous variable transmission according to claim 2, wherein the differential mechanism (22) is a bevel gear type differential mechanism (22), which comprises a pair of side gears (13,15) connected to the corresponding output disks (3,5), pinions (16) meshed with the both side gears (13,15), a differential case (18) rotatably supporting the pinions (16), and output gears (19) secured to the differential case (18) and connected to the output shaft (20). A toroidal continuous variable transmission according to claim 2, wherein the differential mechanism (22) is a planetary gear type differential mechanism. A toroidal continuous variable transmission having: an input shaft (1); a pair of input disks (2,4) that rotate with the input shaft (1); a pair of output disks (3,5) disposed opposite the corresponding input disks (2,4) and rotatably mounted on the input shaft (1); tiltable power rollers (8,9) disposed between the opposing input disks (2,4) and output disks (3,5) to transfer torque from the input disks (2,4) to the output disks (3,5); a differential mechanism (112;126) to drivably connect the output disks (3,5) and an output shaft (139); characterised in that a clutch (113;132) transmits and interrupts torque between the output disks (3,5); and the output shaft (139) is drivably connected to the differential mechanism (112;126). A toroidal continuous variable transmission according to claim 5, wherein the differential mechanism (112) comprises a pair of side gears (114,115), pinions (116) meshed with the both side gears (114,115), a differential case (117) rotatably supporting the pinions (116), and an output gear (118) secured to the differential case (117) and drivably connected to the output shaft (139), and wherein the clutch (113) transmits and interrupts torques between a pair of engagement members (119,120), with one engagement member (119,120) connected to one of the side gears (114,115) and to one of the output disks (3,5) and with the other engagement member (119,120) connected to the other side gear (114,115) and the other output disk (3,5). A toroidal continuous variable transmission according to claim 5, wherein the differential mechanism (126) is a planetary gear mechanism, which comprises a sun gear (127) connected to one of the output disks (3,5), pinions (128,129) connected to the other output disk (3,5) and meshed with the sun gear (127), a carrier (130) supporting the pinions (128,129), and a ring gear (131) meshed with the pinions (128,129) and drivably connected to the output shaft (139), and wherein the clutch (132) transmits and interrupts torques between a pair of engagement members (133,134), with one engagement member (133,134) connected to the sun gear (127) and with the other engagement member (133,134), connected to the carrier (130).

Inventors: INOUE EIJI, INOUE, EIJI
Applicants: ISUZU MOTORS LTD, ISUZU MOTORS LIMITED
Application year: 1996
Main classification: F16H15
IPC codes: F16H61, F16H37, F16H15