Eight speed planetary kinematic arrangement with two rotating clutches

A multiple speed power transmission comprising: four epicyclic gearing assemblies each having first, second, and third rotating elements with specified interconnections, an input shaft connected to one of the rotating elements, an output shaft, two rotating clutches releasably connecting the input shaft to rotating elements, and four brakes selectively holding rotating elements against rotation. Clutches and brakes are applied in combinations of two to produce eight forward ratios and one reverse ratio.

BACKGROUND OF THE INVENTION

This invention relates to the field of automatic transmissions for motor vehicles. More particularly, the invention pertains to a kinematic arrangement of gearing, clutches, brakes, and the interconnections among them in a power transmission.

DETAILED DESCRIPTION OF THE INVENTION

A transmission according to a first embodiment of the present invention is illustrated inFIG. 1. The transmission contains four simple planetary gear set assemblies20,30,40, and50. Each simple planetary gear set assembly has a sun gear, a ring gear with an internal mesh, a planet carrier, and a set of planet gears supported for rotation on the carrier and meshing with both the sun gear and ring gear. A recommended number of gear teeth for each of these gears is shown inFIG. 2.

Gearbox input shaft10is driven by the vehicle's engine via torque converter assembly100. The third sun gear42, is fixed to gearbox input shaft10. The first carrier26is connected to the second sun gear32. The second carrier36is connected to the third ring gear44. The first ring gear24, third carrier46, and fourth ring gear54are mutually connected. A gearbox output shaft12drives the vehicle wheels, preferably via a driveshaft, a differential assembly, and rear axle shafts. Gearbox output shaft12is fixed to the fourth carrier56and the second ring gear34. A transmission case14provides support for the gear sets, input shaft, and output shaft.

Clutches60and62and brakes64,66,68, and70are preferably hydraulically actuated friction clutches which releasably connect two elements when hydraulic pressure is applied and disconnect those elements when the hydraulic pressure is released. Clutch60releasably connects gearbox input shaft10to the first sun gear22. Clutch62releasably connects gearbox input shaft10to the first ring gear24, third carrier46, and fourth ring gear54. Brake64releasably connects the first sun gear22to the transmission case14. Brake66releasably connects the fourth sun gear52to the transmission case14. Brake68releasably connects the first carrier26and second sun gear32to the transmission case14. Brake70releasably connects the second carrier36and the third ring gear44to the transmission case14. One way clutch72is a passive device which allows the second carrier36and third ring gear44to rotate freely in a positive direction but prevents rotation in the opposite direction.

Torque converter assembly100comprises an impeller104that is driven by the transmission input shaft102, stator108, and turbine106. The stator108is connected to the transmission case14by a one way clutch110. When the turbine is substantially slower than the impeller, the one way clutch holds the stator stationary and it provides a reaction torque to create torque multiplication between the impeller and turbine. The one way clutch overruns when the turbine speed is near or greater than the impeller speed. Lock-up clutch112connects the turbine to the impeller eliminating the hydrodynamic losses of the torque converter. InFIG. 1, the turbine is connected to gearbox input shaft12via a spring114. This spring isolates the gearbox and driveline from the torque pulses produced by the engine while transmitting the average torque. A torque converter assembly with a spring in this location is commonly called a turbine damper.

The transmission ratio is selected by applying hydraulic pressure to two of the clutches and brakes as indicated inFIG. 3.

The transmission is prepared for forward motion in first gear by applying brake66. While the vehicle is at rest, turbine106, gearbox input shaft10, and all gear set components are stationary. The engine drives impeller104, which circulates fluid toroidally among the impeller, stator, and turbine. This fluid flow pattern produces a torque on the turbine shaft and gearbox input shaft10. One way clutch72provides a reaction at ring gear44. Clutch66provides another reaction at sun gear52. Thus, a multiple of the input torque is transferred to output shaft12, accelerating the vehicle.

In this condition, one way clutch72will overrun if an attempt is made to transmit power in the opposite direction. If engine braking behavior is desired, it is necessary to also apply friction brake70. Optionally, one way clutch72may be omitted and friction brake70applied for both directions of power transfer.

Lock-up clutch112may be applied any time the speed of gearbox input shaft10is within the engine's operating range. Preferably, it is applied as soon as possible and remains engaged as long as possible in order to minimize transmission parasitic losses.

To shift to second gear, brake68is progressively engaged, maintaining brake66fully applied. As the torque capacity of brake68increases, one way clutch72will overrun. If one way clutch72is omitted, brake70must be progressively released as brake68is engaged.

To shift from second to third gear, brake64is progressively engaged while brake68is progressively released. To shift from third to fourth gear, clutch60is progressively engaged while brake64is progressively released. To shift from fourth to fifth gear, clutch62is progressively engaged while clutch60is progressively released. Brake66is maintained in the fully applied state through all of these transitions.

To shift from fifth to sixth gear, clutch60is progressively engaged while brake66is progressively released. Sixth gear is a direct drive gear. To shift from sixth to seventh gear, brake64is progressively engaged while clutch60is progressively released. To shift from seventh to eighth gear, brake68is progressively engaged while brake64is progressively released. Clutch62is maintained in the fully applied state through all of these transitions.

Downshifting to a lower gear is accomplished by reversing the steps described above for the corresponding upshift.

The transmission is operated in reverse by applying clutch60and brake70.

FIGS. 4,5, and6illustrate alternate embodiments that differ from the above embodiment with respect to the construction and function of torque converter assembly100. These embodiments are operated in the same fashion as the previous embodiment.

In the embodiment ofFIG. 4, a relatively narrow shaft116runs through the center of the gearbox inside gearbox input shaft10, which is hollow. Shafts116and10are connected to each other as far from the input end of the transmission as feasible. The diameter of shaft116is selected just large enough to withstand the maximum anticipated turbine torque (with an appropriate safety factor). As a result of its small diameter and relatively long length, shaft116has considerable torsional compliance and provides isolation from engine pulses (which was accomplished by spring114in the embodiment ofFIG. 1). In this embodiment, turbine106is connected to shaft116as opposed to shaft10. The remaining components and their interconnections are identical to the embodiment ofFIG. 1.

The embodiment ofFIG. 5also uses a narrow shaft116to provide isolation from engine pulses. In this embodiment, however, the turbine is connected to gearbox input shaft10and lock-up clutch112releasably connects transmission input shaft102to shaft116. Shaft116may be designed to withstand engine torque as opposed to turbine torque which is typically much higher. As a result, it has more compliance and provides better isolation.

In the embodiment ofFIG. 6, lock-up clutch112is located within the gearbox portion and releasably connects the narrow shaft116to gearbox input shaft10. Turbine106is connected to gearbox input shaft10. Shaft116is connected to transmission input shaft102. The fluid that actuates clutch112may be fed through output shaft12.

FIGS. 7 and 8illustrate alternate embodiments which differ with respect to the previous embodiments with respect to the construction of the first gear set and its connections. Torque converter assembly100is not shown in these Figures. Any of the variations of torque converter illustrated inFIGS. 1,4,5, and6and described above could be utilized with the gearbox structures illustrated inFIGS. 7 and 8. The embodiments illustrated inFIGS. 7 and 8are operated in the same fashion as the embodiment illustrated inFIG. 1which is described above.

A transmission according to another embodiment of the present invention is illustrated inFIG. 7. The transmission contains one compound planetary gear set assembly80and three simple planetary gear set assemblies30,40, and50. The compound planetary gear set assembly has a sun gear, a ring gear with an internal mesh, a planet carrier, an inner set of planet gears supported for rotation on the carrier and meshing with the sun gear, and an outer set of planet gears supported for rotation on the carrier and meshing with both one of the inner planet gears and the ring gear.

The third sun gear42, is fixed to gearbox input shaft10. The first ring gear84is connected to the second sun gear32. The second carrier36is connected to the third ring gear44. The first carrier86, third carrier46, and fourth ring gear54are mutually connected. Output shaft12is fixed to the fourth carrier56and the second ring gear34. A transmission case14provides support for the gear sets, input shaft, and output shaft.

Clutch60releasably connects gearbox input shaft10to the first sun gear82. Clutch62releasably connects gearbox input shaft10to the first carrier86, third carrier46, and fourth ring gear54. Brake64releasably connects the first sun gear82to the transmission case14. Brake66releasably connects the fourth sun gear52to the transmission case14. Brake68releasably connects the first ring gear84and second sun gear32to the transmission case14. Brake70releasably connects the second carrier38and the third ring gear44to the transmission case14. One way clutch72allows the second carrier36and third ring gear44to rotate freely in a positive direction but prevents rotation in the opposite direction.

A transmission according to another embodiment of the present invention is illustrated inFIG. 8. The transmission contains one compound planetary gear set assembly90and three simple planetary gear set assemblies30,40, and50. The third sun gear42, is fixed to gearbox input shaft10. The first ring gear94is connected to the second sun gear32. The second carrier36is connected to the third ring gear44. The first sun gear92, third carrier46, and fourth ring gear54are mutually connected. Output shaft12is fixed to the fourth carrier56and the second ring gear34. A transmission case14provides support for the gear sets, input shaft, and output shaft.

Clutch60releasably connects gearbox input shaft10to the first carrier96. Clutch62releasably connects gearbox input shaft10to the first sun gear92, third carrier46, and fourth ring gear54. Brake64releasably connects the first carrier96to the transmission case14. Brake66releasably connects the fourth sun gear52to the transmission case14. Brake68releasably connects the first ring gear94and second sun gear32to the transmission case14. Brake70releasably connects the second carrier38and the third ring gear44to the transmission case14. One way clutch72allows the second carrier36and third ring gear44to rotate freely in a positive direction but prevents rotation in the opposite direction.

A transmission embodiment according to this invention contain four epicyclic gearing assemblies, each with three members that rotate around a common axis. In each epicyclic gearing assembly, the speeds of the three elements are linearly related. The second rotating elements is constrained to rotate at a speed which is a weighted average of the speeds of the first and third elements. The weighting factors are determined by the configuration of the epicyclic gearing assembly and the ratios of the numbers of gear teeth. InFIG. 1, all four epicyclic gearing assemblies are simple planetary gearsets. InFIGS. 7 and 8, one of the epicyclic gearing assemblies is a compound planetary gearset. Other types of epicyclic gearing assemblies, such as coplanar gear loops as described in U.S. Pat. Nos. 5,030,184 and 6,126,566, are known and may be substituted without departing from the present invention.

In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that alternate embodiments can be practiced otherwise than as specifically illustrated and described.