Transaxle having chain final drive

A transmission uses a chain and sprocket final drive that provides all final drive torque multiplication in addition to transferring power to the differential axis. The transmission includes a front support structure that provides for a small driving sprocket. The front support includes an insert made of hardened material that can serve as the inner bearing race for the driving sprocket. In some embodiments, four fluid passageways are provided to the torque converter. In some embodiments, the park gear may be integrated with the driven sprocket.

TECHNICAL FIELD

This disclosure related to the field of automotive transmissions. More particularly, the disclosure relates to a transaxle having a chain final drive assembly that provides both axis transfer and torque multiplication.

BACKGROUND

Many vehicles are used over a wide range of vehicle speeds, including both forward and reverse movement. Some types of engines, however, are capable of operating efficiently only within a narrow range of speeds. Consequently, transmissions capable of efficiently transmitting power at a variety of speed ratios are frequently employed. When the vehicle is at low speed, the transmission is usually operated at a high speed ratio such that it multiplies the engine torque for improved acceleration. At high vehicle speed, operating the transmission at a low speed ratio permits an engine speed associated with quiet, fuel efficient cruising.

FIG. 1depicts a typical front wheel drive transaxle10. Flow of mechanical power is shown by solid lines. Power is provided by internal combustion engine12. The crankshaft of engine12drives torque converter14. Torque converter14permits the engine to idle while the vehicle is stationary. Torque converter14transmits the power to gearbox16. In some operating conditions, torque converter14may decrease shaft speed and increase shaft torque. Gearbox14adjusts the speed and torque according to current vehicle requirements. Engine12, torque converter14, and gearbox16are situated on a common axis offset from the axis about which the front wheels18and20rotate. Transaxle10includes axis transfer components22to transfer power from gearbox16to differential24, which is located approximately on the wheel rotation axis. These components may also multiply the torque by a final drive ratio. Differential24transmits the power to left and right wheels18and20while permitting slight speed differences when the vehicle turns a corner.

SUMMARY

According to a first embodiment, a transmission includes a chain engaging first and second sprockets. The first sprocket is supported for rotation about a front support by needle bearings which may roll directly on the front support. The second sprocket is bolted to a differential carrier for rotation therewith. The transmission may also include a turbine shaft supported by the front support. The front support may define first through fourth channels. The first channel may be in fluid communication with an axial channel within the turbine shaft. The second channel may be in fluid communication with a channel defined between the front support and the turbine shaft. The third channel may be fluidly connected to an outer surface of the front support body. The fourth channel may be fluidly connected to a space between the turbine shaft and a turbine shaft insert. The transmission may also include a cast intermediate member fixed to the front support, a bell housing, and a valve body and having channels fluidly connecting the first and second channels of the front support to the valve body. The front support may include a front support body and a front support insert. The front support body may be configured to support the turbine shaft. The front support insert may be fixed to the front support body such that the first and channels go through both the front support body and the front support insert. The transmission may also include a planetary gear set having a sun gear supported for rotation around a portion of the first sprocket, a carrier splined to the first sprocket, a ring gear, and a plurality of planet gears supported for rotation with respect to the carrier and in meshing engagement with the sun gear and the ring gear. A shell may be fixedly coupled to the sun gear and extend between the planetary gear set and the chain. A brake may selective hold the shell against rotation. A park gear may be fixedly coupled to the first sprocket or to the second sprocket.

According to a second embodiment, a transmission includes a bell housing, an intermediate member, a front support body, and a front support insert. The intermediate member is fixed to the bell housing. The front support body is fixed to the intermediate member and is configured to support a turbine shaft. The front support insert is fixed to the front support body and is configured to support a first sprocket. The intermediate member, front support body, front support insert, and turbine shaft define at least two fluid passageways from a valve body to a torque converter. A second sprocket may be bolted to a differential carrier for rotation therewith. A chain may engage the first and second sprockets.

A transmission front support includes a front support body and a hollow front support insert. The front support body is configured to support a turbine shaft. The hollow front support insert is fixed to the front support body and is configured to support a first sprocket. The front support body, front support insert, and turbine shaft define four fluid passageways each fluidly connecting an intermediate member to a torque converter.

DETAILED DESCRIPTION

A group of rotatable elements are fixedly coupled to one another if they are constrained to rotate at the same speed about the same axis in all operating conditions. Rotatable elements may be fixedly coupled by, for example, spline connections, welding, press fitting, or machining from a common solid. Slight variations in rotational displacement between fixedly coupled elements may occur such as displacement due to lash or shaft compliance. In contrast, two rotatable elements are selectively coupled by a shift element when the shift element constrains them to rotate at the same speed about the same axis whenever the shift element is fully engaged and the rotatable elements are free to rotate at distinct speeds in at least some other operating condition. A shift element that holds a rotatable element against rotation by selectively connecting it to the housing is called a brake. A shift element that selectively couples two or more rotatable elements to one another is called a clutch. Shift elements may be actively controlled devices such as hydraulically or electrically actuated clutches or brakes or may be passive devices such as one way clutches or brakes. Two rotatable elements are coupled if they are either fixedly coupled or selectively coupled.

FIG. 2schematically depicts a gearbox16, axis transfer components22, and differential26. This gearing arrangement provides a variety of fixed speed ratios between turbine shaft30and first sprocket32. Turbine shaft30is driven by the torque converter14.

The transaxle ofFIG. 2utilizes four simple planetary gear sets40,50,60, and70. A planet carrier42rotates about a central axis and supports a set of planet gears44such that the planet gears rotate with respect to the planet carrier. External gear teeth on the planet gears mesh with external gear teeth on a sun gear46and with internal gear teeth on a ring gear48. The sun gear and ring gear are supported to rotate about the same axis as the carrier. Gear sets50,60, and70are similarly structured. Turbine shaft30, first sprocket32, and gear sets40,50,60, and70are all supported within transaxle housing34. A suggested ratio of gear teeth for each planetary gear set is listed in Table 1.

Sun gear66is fixedly coupled to turbine shaft30. Ring gear58and carrier72are fixedly coupled to first sprocket32. Ring gear48, carrier62, and ring gear78are mutually fixedly coupled. Carrier42is fixedly coupled to sun gear56. Carrier52is fixedly coupled to ring gear68. Turbine shaft30is selectively coupled to ring gear48by clutch80. Sun gear46is selectively coupled to turbine shaft30by clutch82and selectively held against rotation by brake84. Carrier42and sun gear56are selectively held against rotation by brake86. One way brake88permits carrier52to rotate in one direction but prevents rotation in the opposite direction. Brake90selectively holds carrier52against rotation in either direction. Finally, brake92selectively holds sun gear76against rotation.

As shown in Table 2, engaging the shift elements in specified combinations establishes eight forward speed ratios and one reverse speed ratio between turbine shaft30and first sprocket32. An X indicates that the shift element is required to establish the speed ratio. When the gear sets have tooth numbers as indicated in Table 1, the speed ratios have the values indicated in Table 2. In 1st gear, the transmission transfers power from turbine shaft30to first sprocket32but one way brake88overruns to prevent transfer of power in the opposite direction. The M1 state has the same speed ratio as 1st gear, but is capable of transferring power in either direction.

Chain100wraps around and engages first sprocket32and second sprocket102. Second sprocket102is fixedly coupled to the carrier104of differential24. Second sprocket102is approximately 2.5 times larger in diameter than first sprocket32. Therefore, the chain and sprocket assembly provides both the final drive ratio torque multiplication and the axis transfer functions. A number of beveled planet gears106are supported for rotation with respect to carrier104. Each planet gear meshes with both left and right beveled side gears108and110respectively. Left beveled side gear108is fixedly coupled to left half-shaft112while right beveled side gear110is fixedly coupled to right half-shaft114. Other types of differential gearing are known and may be substituted, such as a differential based on a double pinion planetary gear set with helical gears instead of bevel gears.

Compared to a transaxle that uses a final drive planetary gear set to provide torque multiplication and a chain and sprocket assembly for axis transfer, this arrangement offers several advantages. First, the mesh losses associated with the planetary gear set are eliminated. Elimination of the planetary gear set also reduces cost and space requirements. The chain and sprocket assembly has lower losses than a layshaft gear type final drive assembly.

FIG. 3shows a partial cross section of a first embodiment of a transmission according to the schematic ofFIG. 2. Generating enough final drive ratio with a chain and sprockets requires the first sprocket32to be small in diameter. However, it is still important that the sprocket be properly supported. Turbine shaft30is supported by front support120. First sprocket32is also supported by front support120via bearing122. Conventionally, a bearing would include inner and outer races press fit into the rotating part in addition to the rolling elements themselves. These races require radial space. Front support120is machined from steel such that it is stronger and more dimensionally accurate than a cast part. An outer surface124of front support120is heat treated and machined to a surface finish that permits it to be the inner race for roller bearing122. This reduces the inner diameter of first sprocket32which permits reducing the pitch diameter of first sprocket32.

Front support120is attached to intermediate member126which is attached, in turn, to bell housing128and transmission valve body130. The valve body130may be attached to transmission housing34. Use of intermediate member126minimizes the size and cost of front support120. Intermediate member126may be a cast part.

Fluid is provided from the valve body to torque converter14through two channels in intermediate member126and front support120. Fluid flows into the torque converter through one of the channels and flows out of the torque converter through the other channel. A first portion130of one of these channels is formed into intermediate member126. A second portion132of the channel is formed in front support120. The second of the two channels is formed similarly at a different circumferential location. A hole134is drilled axially in turbine shaft30. A radial hole connects this axial hole to one of the channels in center support120. The other channel is connected to a gap136between center support120and turbine shaft32. In order to engage a torque converter lock-up clutch, the pressure difference between the two channels is reversed.

Park gear138is integrally formed with sprocket32. To engage park, a parking mechanism forces a parking pawl into engagement with park gear138, holding sprocket32stationary. This, in turn, holds differential carrier104stationary.

FIG. 4shows another partial cross section of the first embodiment of a transmission according to the schematic ofFIG. 2, focusing on the differential axis. Second sprocket102is fixedly coupled to differential carrier104by bolt140. Chain100continuously engages second sprocket102.

FIGS. 5 and 6show partial cross sections of a second embodiment of a transmission according to the schematic ofFIG. 2. In this embodiment, park gear138′ is integrally formed with second sprocket102rather than with first sprocket32. Placing the park gear on the differential axis offers several advantages. The axial length of the transmission along the main axis is reduced. Although the axial length along the differential axis may be increased relative to the first embodiment, it is still much shorter than a transmission having a final drive planetary on the differential axis. Furthermore, the chain and sprockets are not park-critical components. Failure of the chain or one of the sprockets would not allow the vehicle to roll while Park is engaged. The maximum distance that the vehicle can move with park engaged must be tightly controlled. Lash in the chain and sprocket mechanism will not contribute to this distance.

FIGS. 7 and 8illustrate an embodiment suitable for a transmission having a four-pass torque converter. In a four-pass torque converter, control of the torque converter lock-up clutch is independent of provision of fluid to the hydrodynamic elements. Additional passageways conduct fluid to an apply chamber and a balance chamber. The fluid supplied to the balance chamber is maintained at close to ambient pressure. The pressure of the fluid supplied to the apply chamber is adjusted by the controller to set the torque capacity of the lock-up clutch. The torque capacity of the lock-up clutch is based on the pressure difference between the apply chamber and the balance chamber. In a three-pass torque converter, the balance chamber is supplied with fluid leaving the hydro-dynamic chamber. The pressure of this fluid can vary in response to actions such as stroking of shifting clutches, making accurate control of lock-up clutch torque capacity more challenging.

The embodiment ofFIGS. 7 and 8provides four separate fluid passageways between the valve body and the torque converter. Whereas front support120ofFIGS. 3 and 5was formed in a single piece, the front support ofFIGS. 7 and 8is formed in two pieces: front support body150and front support insert152. A hollow input shaft insert154is installed into the input shaft to create two channels:134′ on the interior of the input shaft insert and156between the exterior of the input shaft insert and the input shaft30. Outer surface124′ of front support insert152is machined to serve as the inner race for bearing122.

Fluid is routed to the hydrodynamic chamber via channel158in front support body150, axial channel160, radial channel162in front support insert152, and an axial channel between the front support and input shaft30. Fluid is returned from the hydrodynamic chamber via radial channel164in front support body150, axial channel166, and channel168in front support body150. Fluid is supplied to the lock-up clutch apply chamber via channel132′ in front support body150, axial channel170, radial channel172in front support insert152, and channel156. Radial channels in input shaft30connect channel172to channel156and connect channel156to the torque converter turbine housing. Axial channels160,166, and170are formed between front support body150and front support insert152. Fluid is supplied to the lock-up clutch balance chamber via channel174in front support body150, radial channel176in front support insert152, and axial channel134′ in input shaft30.