GB2035479A

GB2035479A - Power transmissions having a directionally sensitive torque- transmitting device

Info

Publication number: GB2035479A
Application number: GB7936402A
Authority: GB
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1978-11-01
Filing date: 1979-10-19
Publication date: 1980-06-18
Also published as: IT7950643A0; FR2440496A1; AU5141479A; AU523432B2; JPS5563045A; CA1105738A; DE2939724A1

Abstract

A torque-transmitting device in a power transmission, having a higher torque capacity in one rotational direction than in the other, includes a one-way drive device 28 in series torque-transmitting relation with a multi-disc friction device 20 so that in one rotational direction of torque transmission both the one- way device and the friction device transmit torque. Additionally, a single- plate friction device 84 is disposed in parallel drive relation with the one-way device so that, on torque reversal, only the single-plate device transmits torque. A single piston is pressurized to simultaneously engage both of the friction devices. <IMAGE>

Description

SPECIFICATION Power transmissions having a directionally sensitive torque-transmitting device This invention relates to power transmissions having a directionaily sensitive torque-transmitting device.

In other words, the device has a higher torque capacity in one rotational direction of torque transmission than in the other.

In power transmissions, a gear ratio change frequently involves engagement of one friction device (a clutch or a brake) with simultaneous disengagement of another friction device. The engagement and disengagement of the respective devices must be controlled and correlated during the ratio change to prevent on the one hand engine flare (run-away) and on the other hand unnecessary transmission tieup. Engine flare occurs, during a ratio change, when the offgoing device releases its controlled element prior to the oncoming device having established sufficient torque-transmitting capacity to accept the input load. If on the other hand the overlap time between the devices is extensive, transmission tie-up can occur, resulting in engine or vehicle stuttering (hesitation).

By the present invention there is provided a transmission including a torque-transmitting device comprising a one-way device having a first member and a second member, and a friction drive-establishing device having a plurality of friction discs selectively connectible to the first member of the one-way device for delivering drive torque by way of the first member of the one-way device to the second member in one direction of rotation, the friction drive-establishing device including at least one friction disc which is selectively engageable with the plurality of friction discs and is connected to the second member of the one-way device for transmitting a predetermined amount of torque from the second member to the friction drive-establishing device upon torque reversal from the one direction of rotation and for permitting slip between the second member of the one-way device and the friction drive-establishing device when the predetermined amount of torque is exceeded, and an apply piston for effecting frictional engagement of all of the friction discs simultaneously.

With such an arrangement it is possible to prevent these conditions of engine flare and transmission tie-up from occurring by the limitation, in one rotational direction, of the maximum torque capacity of one of the devices being interchanged so that tie-up cannot occur, and thus the time required for interchanging the devices is less critical and overlapping of the devices is feasible.

In the accompanying drawing: Figure 1 is a schematic diagram of one embodiment of a power transmission in accordance with the present invention; and Figure 2 is a fragmentary elevation of one embodiment of a torque-transmitting device in conformity with the present invention.

In the drawing, Figure 1 shows a power transmission having an input shaft 10, an output shaft 12, a pair of planetary gear sets 14 and 16, three selectively engageable friction clutches 18, 20 and 22, a pair of selectively engageable friction brakes 24 and 26, and a pair of one-way drive devices 28 and 30. The input shaft 10 has formed thereon a clutch hub 32 which supports an inner drum 34 of the clutch 1 8 and an outer drum 36 of the clutches 20 and 22. The clutches and brakes are actuable by fluid pressure.

The planetary gear set 14 includes a sun gear 38, a ring gear 40, and a planet carrier 42 on which is rotatably mounted a plurality of pinion gears 44 meshing with the sun gear 38 and the ring gear 40. The planetary gear set 1 6 includes a sun gear 46, a ring gear 48, and a planet carrier 50 on which is rotatably mounted a plurality of pinion gears 52 meshing with the sun gear 46 and the ring gear 48. The planet carrier 42 and the ring gear 48 are drivingly connected by way of an intermediate shaft 54 to the output shaft 1 2. The sun gear 46 is connected by way of a shaft 56 and a hub 58 to an outer drum 60 of the clutch 18.The ring gear 40 is connected by way of a hub 62 and an intermediate sleeve shaft 64 to the carrier 50, which in turn is connected to an outer race 66 of the one-way device 30 and also to a drum 68 which is operatively associated with the brake 26. The ring gear 40 is also connected to an inner clutch hub 70 of the clutch 22. An inner race 72 of the one-way device 30 is connected to a transmission housing 74.

The clutch 20 has a plurality of plates 75 connected to an inner clutch drum 76 which is also connected to an outer race 78 of the one-way device 28. The one-way device 28 has an inner race 80 which is connected by way of a shaft 82 to the sun gear 38, and is also connected to a single plate 84 of the clutch 20. Interleaved with the plates 75 and with the plate 84 is a plurality of plates 85 that are splined to the outer drum 36.

The transmission gearing and the operation thereof are similar to what is shown in our United States Patent 4,086,827 (Chana). By selective engagement of comuinations of the various clutches and brakes, four forward ratios and a reverse ratio can be established between the input shaft 10 and the output shaft 1 2. With the particular gearing shown, the highest forward ratio is an overdrive ratio, and is obtained by engagement of the clutch 22 and the brake 24. The clutch 22 connects the input shaft 10 to drive the carrier 50 of the planetary gear set 16, and the brake 24 prevents rotation of the sun gear 46 by holding stationary the outer drum 60, the hub 58 and the shaft 56, whereby the output ring gear 48 is caused to rotate at an overdrive ratio.

The third forward ratio is a direct-drive ratio, and is obtained by engagement of both the clutches 20 and 22. On forward torque transmission, the one-way device 28 transmits the torque input from the clutch 20 to the sun gear 38, and the clutch 22 transmits input torque to the ring gear 40, so that the planetary gear set 14 is locked up in a 1:1 ratio.

The single plate 84 of the clutch 20 provides a continuous drive connection between the sun gear 38 and the input shaft 10 with the clutch 20 engaged, such that during coasting in the direct-drive ratio, engine braking is available.

To produce an upshift from the third ratio to the fourth ratio, the brake 24 is engaged, and when this brake has sufficient capacity to permit the interchange to proceed, there is a tendency for the sun gear 38 to rotate faster than the input shaft 10. The one-way device 28 would normally permit the sun gear 38 to overrun, but with the construction described the single plate 84 of the clutch 20 establishes a torque transmitting connection bypassing the one-way device 28 such that the sun gear 38 will not overrun the input shaft 10 until the brake 24 has sufficient capacity to overcome the residual capacity of the single plate 84 and so permit the interchange to proceed. The clutch 20 is fully disengaged only after the ratio change is complete.

To produce a downshift from the fourth ratio to the third ratio, the clutch 20 is engaged whilst the brake 24 is disengaged.

However, the overlap timing is not critical since the single plate 84 will permit slip within the clutch 20 during the shift interchange to permit a smooth ratio change even though the clutch 20 has more torque capacity than is considered desirable for a smooth ratio interchange because of the action of the one-way device 28.

In Figure 2 of the drawing, there is shown in input shaft 10' and an output shaft 82'.

Intermediate these shafts 10' and 82', there is a friction clutch 20' and a one-way device 28'. The clutch 20' includes a housing 86 which is drivingly connected to the shaft 10' and has slidably disposed therein a fluidoperable piston 88. The clutch 20 also has an inner drum 90 which serves as the outer race for the one-way device 28'. The one-way device 28' has an inner race 92 drivingly connected to the output shaft 82', and this inner race 92 has formed thereon a spline surface 94 to which is drivingly connected a single clutch plate (disc) 96. The single clutch plate 96 constitutes a member of the clutch 20'.

A plurality of friction plates (discs) 98 are splined at 100 to the inner surface of the clutch housing 86, and a plurality of clutch plates 102 are splined at 104 to the inner drum 90. The clutch plates 98 and 102 are spaced alternately and, together with the clutch plate 96, are limited in respect of movement to the right by a backing plate 106 which is splined to the clutch housing 86. The piston 88 co-operates with the clutch housing 86 to form a clutch apply chamber 108 which is arranged to be selectively pressurized with hydraulic fluid, and depressurized, in the conventional manner. When the chamber 108 is pressurized, the piston 88 is moved into abutting relationship with one of the plates 98, and causes frictional engagement of the adjacent plates 98 and 102 and simultaneous frictional engagement of the plate 96.The one-way device 28' is capable of transmitting torque in one direction only, such that when torque is transmitted from the shaft 1 0' to the shaft 82', the one-way device 28' is operative. This is termed the forward direction of torque transmission.

On a torque reversal, such that torque is being transmitted from the shaft 82' to the shaft 10', the one-way device 28' is inoperable, and with the clutch 20' engaged all the torque must be transmitted through the single plate 96. It is thus evident that the combination of the clutch 20' and the one-way device 28' has a high torque capacity in the forward torque-transmitting direction, but a low torque capacity in the reverse torque-transmitting direction. The relation between the torque capacities in the forward and reverse directions is controlled by the number of plates in the respective sections of the clutch 20'. If the device is desired to transmit, on torque reversal, 50% of the forward torque, the number of friction plates connected to the outer race 90 of the one-way devices 28' will be chosen to be equal to the number of clutch plates that bypass the one-way device 28'. In other words, the ratio of the number of clutch plates bypassing the one-way device to the total number of plates in the clutch establishes the directional capacity ratio of the clutch.

The application of this principle is not limited to friction clutches: it is also valid for a disc-type (plate-type) friction brake.

The above-described torque-transmitting device thus acts in a similar way to a doublewrap band which has one level of torque capacity in the self energizing direction of rotation and a lower level of torque capacity in the opposite direction of rotation.

Claims

1. A transmission including a torque-transmitting device comprising a one-way device having a first member and a second member, and a friction drive- establishing device having a plurality of friction discs selectively connectible to the first member of the one-way device for delivering drive torque by way of the first member of the one-way device to the second member in one direction of rotation, the friction drive-establishing device including at least one friction disc which is selectively engageable with the plurality of friction discs and is connected to the second member of the one-way device for transmitting a predetermined amount of torque from the second member to the friction drive-establishing device upon torque reversal from the one direction of rotation and for permitting slip between the second member of the one-way device and the friction drive-establishing device when the predetermined amount of torque is exceeded, and an apply piston for effecting frictional engagement of all of the friction discs simultaneously.

2. A transmission according to claim 1, in which the first and second members of the one-way device comprise an input member and an output member respectively, the said one direction of rotation comprises a forward direction of rotation, and the friction driveestablishing device includes a single friction disc as aforesaid selectively engageable with the plurality of friction discs and connected to the output member of the one-way device.

3. A transmission according to claim 2, having gearing providing a direct drive ratio and an overdrive ratio, and including a planetary gear set having a first gear member driven at input speed during both drive ratios, a second gear member driven at input speed during the direct drive ratio and at a speed greater than input speed during the overdrive ratio, and a third member connected to output means, a drive clutch including a one-way device as aforesaid with the output member drivingly connected to the second gear member, a friction drive-establishing device as aforesaid selectively drivingly connectible between input means and the input member of the one-way device for delivering forward drive torque by way of the one-way drive device to the second gear member, a single friction disc as aforesaid selectively drivingly connectible between the output member of the one-way device and the input means for transmitting a predetermined amount of reverse torque less than the forward drive torque from the second gear member to the input means during a drive reversal in the planetary gear set and for permitting a speed differential between the second gear member and the input means when the predetermined amount of reverse torque is exceeded, and means for fluid operation of the apply piston for selectively effecting frictional engagement and disengagement of the plurality of friction discs and the single friction discs simultaneously.

4. A transmission substantially as hereinbefore particularly described and as shown in Figure 1 of the accompanying drawing.

5. A transmission substantially as hereinbefore particularly described and as shown in Figure 2 of the accompanying drawing.