Abstract:
A multiple speed power transmission comprising: four epicylic gearing assemblies each having first, second, and third rotating elements with specified interconnections, an input shaft, an output shaft, three clutches, and two brakes. Clutches and brakes are applied in combinations of three to produce eight forward ratios and one reverse ratio.

Description:
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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a transmission which produces eight forward speed ratios and one reverse speed ratio. 
         FIG. 2  is a table showing the proposed tooth numbers for the gears of the transmission illustrated in  FIG. 1 . 
         FIG. 3  is a table indicating the states of the clutches and resulting speed ratio of the transmission in  FIG. 1  when the gears have the number of teeth indicated in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A transmission according to the present invention is illustrated in  FIG. 1 . Input shaft  10  is driven by the vehicle&#39;s engine, preferably via a torsional damper that absorbs combustion pulses. Output shaft  12  drives the vehicle wheels, preferably via a driveshaft, a differential assembly, and rear axle shafts. A transmission case  14  provides support for the gear sets, shafts, clutches, and brakes. 
     The transmission contains four simple planetary gear set assemblies  20 ,  30 ,  40 , and  50 . Each simple planetary gear set assembly has a sun gear, a ring gear with an internal gear mesh, a planet carrier, and a set of planet gears supported for rotation on the carrier and meshing with both the sun gear and the ring gear. A recommended number of gear teeth for each of these gears is shown in  FIG. 2 . 
     Input shaft  10  drives sun gear  52  and planet carrier  46 . Output shaft  12  is driven by ring gear  54 . Carrier  26  is connected to carrier  56 , ring gear  24  is connected to carrier  36 , and ring gear  34  is connected to ring gear  44 . 
     Brakes  60  and  62  and clutches  64 ,  66 , and  68  are 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. Brake  60  releasably connects sun gear  32  to the transmission case  14 . Brake  62  releasably connects sun gear  22  to the transmission case  14 . Clutch  64  releasably connects carrier  26  and carrier  56  to ring gear  34  and ring gear  44 . Clutch  66  releasably connects ring gear  24  and carrier  36  to sun gear  42 . Clutch  68  releasably connects sun gear  32  to sun gear  42 . 
     The transmission ratio is selected by applying hydraulic pressure to three of the clutches and brakes as indicated in  FIG. 3 . 
     The transmission is prepared for forward motion in first gear by applying brake  62  and clutch  66 . To launch the vehicle, brake  60  is gradually engaged. Alternatively, the transmission may be equipped with a launch device such as a torque converter or a dedicated launch clutch. If the transmission is so equipped, it is prepared for forward motion by applying brakes  60  and  62  and clutch  66  and launching the vehicle using the launch device. 
     To shift to second gear, clutch  68  is progressively engaged while clutch  66  is progressively released, maintaining brakes  60  and  62  fully applied. To shift from second to third gear, clutch  66  is progressively engaged while brake  60  is progressively released, maintaining brake  62  and clutch  68  fully applied. To shift from third to fourth gear, clutch  64  is progressively engaged while clutch  66  is progressively released, maintaining brake  62  and clutch  68  fully applied. To shift from fourth to fifth gear, clutch  66  is progressively engaged while clutch  68  is progressively released, maintaining brake  62  and clutch  64  fully applied. To shift from fifth to sixth gear, clutch  68  is progressively engaged while brake  62  is progressively released, maintaining clutches  64  and  66  fully applied. To shift from sixth to seventh gear, brake  60  is progressively engaged while clutch  68  is progressively released, maintaining clutches  64  and  66  fully applied. Finally, to shift from seventh to eighth gear, clutch  68  is progressively engaged while clutch  66  is progressively released, maintaining brake  60  and clutch  64  fully applied. 
     Downshifting to a lower gear is accomplished by reversing the steps described above for the corresponding upshift. 
     The transmission is prepared for reverse motion by applying brake  62  and clutch  64 . To launch the vehicle, brake  60  is gradually engaged. If the transmission is equipped with a launch device, it is prepared for reverse motion by applying brakes  60  and  62  and clutch  64  and launching the vehicle using the launch device. 
     A transmission embodiment according to this invention contains 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. In  FIG. 1 , all four epicyclic gearing assemblies are simple planetary gear sets. Other types of epicyclic gearing assemblies include double pinion planetary gear sets, stepped pinion planetary gear sets, and coplanar gear loops as described in U.S. Pat. Nos. 5,030,184 and 6,126,566. Other types of epicyclic gearing assemblies may be substituted without departing from the present invention. 
     In accordance with the provisions of the patent statutes, the structure and operation of the preferred embodiment has been described. However, it should be noted that alternate embodiments can be practiced otherwise than as specifically illustrated and described.