Multiple-speed automatic transmission

A multiple speed transmission having an input and output includes a first and second planetary gearsets, each gearset including a sun gear, a ring gear surrounding the sun gear, a set of planet pinions meshing with the sun gear and the ring gear, and a carrier on which the planet pinions are rotatably supported, the carrier of the first gearset being driveably connected to the ring gear of the second gearset. A third gearset, driveably connected to the carrier of the second gearset and the ring gear of the first gearset, alternately drives the output at a predetermined lower speed relative to a speed of the carrier of the second gearset, and driving the output at substantially the speed of the ring gear of the first gearset. A first clutch connects and disconnects the input and the sun gear of the first gearset. A second clutch connects and disconnects the input and the sun gear of the second gearset. A third clutch alternately connects and disconnects the input and the carrier of the first gearset. An overrunning brake holds the carrier of the first gearset against rotation on the transmission housing and releases the carrier of the first gearset. A first brake holds the sun gear of the first gearset against rotation on the transmission housing and releases the sun gear of the first gearset. A second brake holds the carrier of the first gearset against rotation on the housing and releases the carrier of the first gearset.

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 such transmissions.

The number of forward drive speed ratios in automatic transmissions for motor vehicle has continued to increase due to the need to increase fuel economy and to avoid large steps between the speed ratios. Each known six-speed transmission in which no more than three gearsets and five friction elements (the clutches and brakes that control operation of the transmission) are employed has some drawbacks such as ratio progression, shared pinions, etc.

U.S. Pat. No. 5,106,352 describes a multi-speed automatic transmission for motor vehicles that includes two parallel gearsets providing two fixed speed ratios. The second speed ratio is higher than the first speed ratio. A first power path using the first fixed speed ratio includes a first control clutch and a second control clutch, and a second power path using the second fixed speed ratio includes a third control clutch. Several embodiments of the transmission include a double planetary gearset; other embodiments disclose a Ravigneaux gearset, a first control brake and a second control brake. Alternatively, the input shaft and output shaft are in alignment and one of the two speed ratios is a direct drive.

Experience in manufacturing Ravigneaux gearsets for automatic transmissions has shown that these gearsets tend to produce relatively high gear noise in comparison to simple planetary gearsets and Simpson gearsets. To minimize gear noise, extensive steps are taken during the manufacturing process to grind the gears. But these steps and the additional complexity associated with assembling Ravigneaux gearsets add cost to the transmission.

There is a need for a six-speed automatic transmission in which the planetary gearsets are entirely simple planetary gearsets rather than double pinion gearsets or shared pinion gearsets. Preferably such a transmission would require no more than five hydraulically-actuated friction clutches and brakes to produce step changes among the speed ratios.

SUMMARY OF THE INVENTION

A multiple speed transmission according to the present invention having an input and output includes first and second planetary gearsets, each gearset including a sun gear, a ring gear surrounding the sun gear, a set of planet pinions meshing with the sun gear and the ring gear, and a carrier on which the planet pinions are rotatably supported, the carrier of the first gearset being driveably connected to the ring gear of the second gearset. A third gearset, driveably connected to the carrier of the second gearset and the ring gear of the first gearset, alternately drives the output at a predetermined lower speed relative to a speed of the carrier of the second gearset, and driving the output at substantially the speed of the ring gear of the first gearset. A first clutch connects and disconnects the input and the sun gear of the first gearset. A second clutch connects and disconnects the input and the sun gear of the second gearset. A third clutch alternately connects and disconnects the input and the carrier of the first gearset. An overrunning brake holds the carrier of the first gearset against rotation on the transmission housing and releases the carrier of the first gearset. A first brake holds the sun gear of the first gearset against rotation on the transmission housing and releases the sun gear of the first gearset. A second brake holds the carrier of the first gearset against rotation on the housing and releases the carrier of the first gearset.

A transmission mechanism according to this invention uses only simple planetary gearsets, as opposed to double pinion gearsets or shared pinion gearsets. A front wheel drive embodiment uses only two simple planetary gearsets and an additional gear pair, whereas most arrangements require three simple gearsets or a simple gearset and a Ravigneaux gearset.

The transmission can be applied readily to a vehicle powertrain for which it is an advantage to provide alternately one overdrive speed ratio and two overdrive speed ratios, each application having a direct drive speed ratio.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring toFIG. 1, an automotive powertrain includes an engine10or other power source and a torque converter11, which produces a fluid drive connection30between the engine and an automatic, step-change transmission12through an input shaft14. The output16of the transmission is drivebly connected to a final drive gearset, which includes a final drive pinion18supported on the output shaft16, and a final drive gear20in continuous meshing engagement with the final drive pinion18.

Transmission12includes the first simple planetary gearset22, which includes a sun gear24journalled on the input14, a ring gear26surrounding the sun gear and having its center on input14, a first set of planet pinions28in continuous meshing engagement with sun gear24and ring gear26and rotatably supported on a carrier30.

A second simple planetary gearset32, arranged coaxially with the first gearset22and input14, includes a sun gear34, journalled on input14, ring gear36surrounding sun gear34, a set of planet pinions38in continuous meshing engagement with sun gear34and ring gear36and rotatably supported on a carrier40.

A third gear unit42includes two layshaft gear pairs. The first pair includes a pinion44in continuous meshing engagement with a gear46; the second gear pair includes a pinion48in continuous meshing engagement with a gear50. Both gears46and50are secured to the output16, and they drive the final drive pinion18.

The input14is driveably connected and disconnected alternately to sun gear34through operation of a clutch54. Input14is driveably connected and disconnected alternately to sun gear24through operation of a clutch56. Similarly, input14is driveably connected and disconnected alternately to the carrier30through operation of a clutch58. Sun gear24is grounded or held against rotation on the transmission housing72through connecting member76when brake74is applied. A one-way brake (OWB)78holds carrier30against rotation on housing72when the brake78produces a drive connection, and disconnects carrier30from the housing72when the brake78overruns.

Beta is the ratio of the ring gear/sun gear tooth ratios for the first and second gearsets22,32(R1/S1, and R2/S2), respectively. Beta, for the second gearset22is 2.630. The table ofFIG. 2shows the combinations of engagements for the torque-transmitting mechanisms that establish six forward speed ratios and one reverse speed ratio between the input14and the output shaft16.

The transmission12operates in the first forward ratio when clutch54is engaged. This causes one-way brake78to produce a drive connection between carrier30and the housing72and to hold carrier30and ring gear36against rotation. With the input14driving sun gear34and ring gear36held to provide a torque reaction, carrier40and pinion48are driven at a slower speed than that of input14. The third gearset produces an additional speed reduction through pinion48and gear50. The ratio of the speed of output16to the speed of input14is 0.206 when the gears and pinions are sized as shown in the example ofFIG. 3.

An upshift to the second speed ratio is produced by maintaining clutch54engaged and engaging brake74. These actions cause OWB78to overrun, and sun gear24to be held against rotation on the housing72. Carrier40and pinion48are underdriven at a speed ratio of 0.491 with respect to the speed of input14, and output gear50is underdriven compared to the speed of pinion48. The output speed ratio is 0.366 when the gears and pinions are sized as shown in the example ofFIG. 3.

An upshift to the third forward speed ratio is produced by maintaining clutch54engaged, disengaging brake74, and engaging clutch56. OWB78overruns, and ring gear36is driveably connected to carrier30. The output is taken at carrier40and pinion48, which rotate at 0.755 times the speed of input14. An additional speed reduction occurs in the third gearset42, causing the output16to rotate at 0.563 times the speed of the input, when the gears and pinions are sized as shown inFIG. 3.

An upshift to the fourth speed ratio occurs when clutch54remains engaged, clutch56is disengaged, and clutch58is engaged. With the control elements in these states, OWB78overruns, sun gear34and ring gear36of the second planetary gearset32rotate at the speed of the input; therefore, carrier40rotates at the speed of input14, a direct drive condition. Ring gear26and pinion44rotate at 0.761 times the speed of input14. The output16rotates at 0.746 times the speed of input14, when the gears and pinions are sized as shown inFIG. 3, due to the speed reduction that occurs in the third gearset42between pinion48and gear50.

An upshift to the fifth speed ratio occurs when clutch54is disengaged, clutch56is engaged, and clutch58remains engaged. With the control elements in these states, OWB78overruns, and sun gear24and carrier30rotate at the speed of input14, which action locks up the first gearset22and causing ring gear26and pinion44to rotate at the speed of input14. A speed reduction occurs in the third gearset42, causing gear46and output to16to rotate at 0.98 times the speed of input14due to the speed reduction that occurs in the third gearset42between pinion44and gear46.

An upshift to the sixth speed ratio occurs when clutch56is disengaged, brake74is engaged, and clutch58remains engaged. With the control elements in these states, OWB78overruns, and carrier30and ring gear36are driven at the speed of input14, and sun gear24is held against rotation on the transmission housing72due to the engagement of brake74. Ring gear26and pinion44are overdriven 1.257 times the speed of input14. The speed reduction that occurs in the third gearset42between pinion44and gear46causes gear46and output16to rotate at 1.232 times the speed of input14.

Reverse drive is produced by engaging clutch56and brake80. When the control elements are in these states, OWB78free wheels, neither overrunning nor driving because carrier30is held against rotation on the transmission housing72due to engagement of brake80. Sun gear24rotates at the speed of input14. A speed reduction occurs in the first gear set22causing ring gear26and pinion44to rotate opposite the direction of input14and at 0.257 times the speed of input14. Due to the speed reduction that occurs in the third gearset42between pinion44and gear46, output16and gear46rotate at 0.252 times the speed of input14when the gears and pinions are sized as shown inFIG. 3.

Alternatively, OWB78may be omitted from this transmission. If OWB78is omitted, the transmission is operated in the first forward speed ratio by engaging clutch54and brake80. In this instance, to shift from the first speed ratio to the second speed ratio, clutch54remains engaged while brake80is released and brake74is engaged. The remainder of the operation is identical to the above description.

Turning now toFIG. 4in which components identical to those inFIG. 1have been marked with the same identifying numerals, a third planetary gearset90includes a sun gear92journalled on an output94, a ring gear96surrounding the sun gear92, and a set the planet pinions98in continual meshing engagement with sun gear92and ring gear96and supported rotatably on a carrier100. Sun gear92is held against rotation on transmission housing72by connecting element102. Carrier100is driveably connected by connecting element104to ring gear26. Ring gear96is driveably connected to carrier40and to output94by the connecting element106.

A hydraulically-actuated brake band108alternately holds carrier30against rotation on the transmission housing72and releases carrier30to rotate freely. When brake band108is applied, connecting member109is frictionally engaged by the brake band and held on the transmission housing72. Carrier30is driveably connected to OWB78and connecting member109by connecting member110.

Referring now toFIGS. 4-6, the transmission ofFIG. 4operates in the first forward speed ratio by engaging clutch54, which causes OWB78to produce a drive connection between carrier30and housing72, thereby holding carrier30and ring gear36against rotation. With sun gear34driven at the speed of input14and ring gear36providing a torque reaction, carrier40and ring gear96are underdriven in relation to the speed of input14at 0.307 times the speed of input14, when the gears and pinions of the planetary gear sets are sized as shown inFIG. 6.

An upshift to the second speed ratio occurs by maintaining clutch54and engaging brake74, which causes OWB78to overrun and holds sun gear24against rotation. Sun gear34is driven at the speed of input14, and sun gears24and92are held against rotation. Speed reduction is produced such that carrier40, ring gear96and output94rotate at 0.528 times the speed of input14when the gears and pinions are sized as shown inFIG. 6.

An upshift to the third speed ratio occurs by maintaining clutch54engaged, engaging clutch56, and disengaging brake74, which causes OWB78to overrun and driveably connects sun gears24and34to input14. Speed reduction is produced which causes carrier40, ring gear96, and output94to be driven at 0.768 when the transmission components are sized as shown inFIG. 6.

An upshift to the fourth speed ratio is produced by maintaining clutch54engaged, disengaging clutch56, engaging clutch58, which causes one-way brake78to overrun and driveably connects the sun gear34and ring gear36of the second gearset32to the input14. This locks-up gearset32causing its carrier40, ring gear96, and output94to rotate at the speed of input14, a direct drive condition.

At first overspeed ratio is produced in the fifth gear by disengaging clutch54, engaging clutch56, and maintaining clutch58engaged, thereby causing one-way brake78to overrun. With carrier30and sun gear24of the first planetary gear set22rotating at the speed of input14, ring gears26and36and carrier100also rotate at the speed of input14. Carrier40, ring gear96, and output94are overdriven at 1.323 times the speed of input14when the components of the gear sets are sized as shown inFIG. 6due to the speed increase that occurs in the third gearset90.

A second overspeed condition occurs in the sixth gear upon maintaining clutch58engaged, disengaging clutch56, and engaging brake74which causes one-way brake78to overrun. With the control elements so disposed, OWB78overruns, sun gear24is held against rotation due to the engagement of brake74, and carrier30and ring gear36rotate at the speed of input14. A speed increase occurs in gearset22due to sun gear24being held against rotation, thereby causing ring gear26and carrier100to rotate at 1.252 times the speed of input14. With sun gear92held fixed against rotation and carrier100being drive by ring gear26, ring gear96and output94rotate at 1.656 times the speed of input14due to the speed increase that occurs in the third gearset90when the components of the gear sets are sized as shown inFIG. 6.

The transmission ofFIG. 4operates in reverse drive upon engaging clutch56and brake band108, which causes carrier30to be held against rotation. A first speed reduction in a first direction occurs in the first gearset22with carrier30held against rotation and sun gear24rotating at the speed of input14. Ring gear26and carrier100rotate in the reverse direction at 0.252 times the speed of input14. A speed increase occurs in the third planetary gearset90due to its sun gear92being fixed against rotation. Therefore, ring gear96and output94are driven at −0.334 times the speed of input14when the components of the gear sets are sized as shown inFIG. 6.

Turning now to the transmission shown inFIG. 7, wherein the same components as those ofFIG. 4are marked with the identical reference numbers, carrier30is driveably connected to one-way brake78through connecting member110, connecting member112driveably connects carrier100of the third gear unit90to the output94, and connecting member114driveably connects carrier40of the second gear unit32to the ring gear96.

The transmission ofFIG. 7produces the first speed ratio by engaging clutch54and disengaging the other friction control elements, which connects sun gear34to the input14, and causes overrunning brake78to produce a drive connection between carrier30and the transmission housing72. A first speed reduction is produced in the second gear unit32due to its ring gear36being held fixed against rotation and sun gear34being driveably connected to the input14. Carrier40is underdriven in relation to the speed of input14. A second speed reduction occurs in the third gearset90due to its ring gear96being driven at the speed of carrier40at 0.316 times the speed of input14, and its sun gear92being fixed against rotation. Carrier98and output94rotate at 0.226 times the speed of input14with the pinions and gears sized as shown inFIG. 9.

An upshift to the second speed ratio is produced by maintaining clutch54engaged and engaging brake74, which causes overrunning brake78to overrun and holds sun gear24fixed against rotation. With the friction control elements so disposed, sun gear24and sun gear92fixed against rotation, and sun gear34rotating at the speed of input14, carrier100and output94rotate at 0.358 times the speed of input14with the pinions and gears sized as shown inFIG. 9.

An upshift to the third forward speed ratio occurs by maintaining clutch5415engaged, disengaging brake74, and engaging clutch56, which causes one-way brake78to overrun. With sun gear92fixed against rotation and sun gears24and34rotating at the speed of input14, carrier100and output94rotate at 0.547 times the speed of input14when the components of the gearsets are sized as shown inFIG. 9.

An upshift to the fourth speed ratio occurs by maintaining clutch54engaged,20disengaging clutch56, and engaging clutch58, which causes one-way brake78to overrun. Sun gear92is fixed to the transmission housing72providing a torque reaction. The second gearset32is locked-up due to its sun gear34being driveably connected through clutch54to input14and its ring gear36being driveably connected to the input through clutch58. A speed reduction occurs in the third gearset90, whose ring gear96rotates at the speed of input14and whose sun gear92is fixed against rotation. Therefore, carrier100is and output94rotate at0.714times the speed of input14when the components of the gearsets are sized as shown inFIG. 9.

The transmission operates in direct drive in the fifth gear ratio upon disengaging clutch54, engaging clutch56, and maintaining clutch58engaged so that one-way brake78overruns. With the friction control element so disposed, the first gearset22is locked-up because sun gear24and carrier30are driveably connected to input14through clutches56and58, respectively. Therefore, ring gear26, and carrier100and output94rotate at the speed of input14.

The transmission ofFIG. 7is upshifted to an overdrive speed when clutch56is disengaged,58remains engaged, and brake74is engaged, thereby causing OWB78to overrun and holding sun gear24fixed against rotation. With the friction control element so disposed, carrier30rotates at the speed of input14and a speed increase occurs in the first gearset22causing ring gear26, carrier100and output94to rotate at 1.323 times the speed of input14when the gears and pinions are sized as shown inFIG. 9.

The transmission ofFIG. 7operates in reverse drive when clutch56is engaged and brake band108is engaged. These actions cause one-way brake78to freewheel and sun gear24to be held fixed due to the engagement of brake band108. A reverse speed reduction occurs in the first gearset22such that ring gear26, carrier100, and output94rotate in the reverse direction at −0.323 times the speed of input14.

The friction control elements55,56,58are preferably torque-transmitting devices of the rotating type, commonly termed clutches. These devices are hydraulically-actuated friction devices well known in the art of power transmissions. The friction control element74is preferably a hydraulically-actuated torque-transmitting device of the stationary type, commonly termed a brake and also well known in the art. The brake74and clutches55,56,58are preferably disc-type brakes. The brake108is preferably a hydraulically-actuated torque-transmitting device of the stationary type, commonly termed a band brake, in which the friction surface of a band surrounds a brake drum and alternately engages and disengages the drum. The OWB78is an overrunning brake, preferably a mechanical device produce a drive connection between its input and output depending on the relative speeds of the input and output. Rollers, sprags, rockers, pawls, etc, located between the input and output may be used to produce the drive connection.