Automatic transmission and a dog clutch for an automatic transmission

A dog clutch for an automatic transmission includes a shape-memory alloy shifter. The shape-memory alloy shifter is configured for moving a sliding clutch along an axial direction between an engaged configuration and a disengaged configuration. A plurality of splines of a mating clutch meshes with a plurality of splines of the sliding clutch in the engaged configuration. A related automatic transmission is also provided.

FIELD OF THE INVENTION

The present subject matter relates generally to automatic transmissions and shifting elements for automatic transmissions.

BACKGROUND OF THE INVENTION

Automatic transmissions generally include at least one planetary gear set and a plurality of shift elements. The shift elements selectively engage components of the planetary gear sets in order to hinder or prevent rotation of the components. Selective actuation of the shift elements adjusts the gear ratio of the automatic transmission and shifts the automatic transmission between its various gears.

Certain automatic transmissions include dog clutch shifting elements. During various gear shifts, the dog clutch is engaged or closed. Engaging the dog poses certain challenges. For example, certain dog clutches are hydraulically actuated. However, creating and maintaining the hydraulic pressure necessary to actuate the dog clutch can be difficult. In addition, hydraulically actuated dog clutches can require compliance with strict cleanliness guidelines in order to prevent debris from negatively affecting performance of the dog clutch. Further, hydraulically actuated dog clutches generally include O-rings, drilled passageways through cast materials and other components that can necessitate a complex transmission design.

Accordingly, an automatic transmission with features for assisting with actuating a shifting element of the automatic transmission would be useful. In particular, a dog clutch with features for assisting with actuating the dog clutch without hydraulic fluid would be useful.

BRIEF DESCRIPTION OF THE INVENTION

The present subject matter provides a dog clutch for an automatic transmission. The dog clutch includes a shape-memory alloy shifter. The shape-memory alloy shifter is configured for moving a sliding clutch along an axial direction between an engaged configuration and a disengaged configuration. A plurality of splines of a mating clutch meshes with a plurality of splines of the sliding clutch in the engaged configuration. A related automatic transmission is also provided. Additional aspects and advantages of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the invention.

In a first exemplary embodiment, an automatic transmission is provided. The automatic transmission includes a plurality of planetary gear sets and a plurality of shifting elements, including a dog clutch that defines an axial direction. The dog clutch includes a clutch support and a sliding clutch mounted to the clutch support. The sliding clutch defines a plurality of splines. A shape-memory alloy shifter is coupled to the sliding clutch. The shape-memory alloy shifter is configured for moving the sliding clutch along the axial direction between an engaged configuration and a disengaged configuration. A mating clutch is mounted to a gear of the plurality of planetary gear sets. The mating clutch defines a plurality of splines. The plurality of splines of the mating clutch meshes with the plurality of splines of the sliding clutch in the engaged configuration. The plurality of splines of the mating clutch is not meshed with the plurality of splines of the sliding clutch in the disengaged configuration.

In a second exemplary embodiment, a dog clutch for an automatic transmission is provided. The dog clutch includes a clutch support and a sliding clutch mounted to the clutch support. The sliding clutch defines a plurality of splines. A shape-memory alloy shifter is coupled to the sliding clutch. The shape-memory alloy shifter is configured for moving the sliding clutch along an axial direction between an engaged configuration and a disengaged configuration. A mating clutch defines a plurality of splines. The plurality of splines of the mating clutch meshes with the plurality of splines of the sliding clutch in the engaged configuration. The plurality of splines of the mating clutch is not mesh with the plurality of splines of the sliding clutch in the disengaged configuration.

DETAILED DESCRIPTION

FIG. 1provides a schematic view of an automatic transmission10according to an exemplary embodiment of the present subject matter. Automatic transmission10may be constructed or arranged in a similar manner to the automatic transmission described in U.S. Pat. No. 8,398,522 to Bauknecht et al., which is hereby incorporated by reference for all purposes. Automatic transmission10may be used in any suitable vehicle. For example, automatic transmission10may be used in a passenger vehicle, such as a car, truck or sport utility vehicle (SUV). Automatic transmission10is configured for selectively adjusting a gear ratio of automatic transmission10, as will be understood by those skilled in the art, in order to provide a suitable mechanical advantage to propel the associated vehicle.

As may be seen inFIG. 1, automatic transmission10includes an input shaft12and an output shaft14. Input shaft12may be coupled to a turbine of a torque converter in order to link automatic transmission10to a motor of an associated vehicle. Output shaft14may be coupled a front axle drive shaft of the associated vehicle. Automatic transmission10may change gears in order to adjust the gear ratio between the motor and front axle drive shaft of the associated vehicle, as will be understood by those skilled in the art.

Automatic transmission10also includes four planetary gear sets: a first planetary gear set20; a second planetary gear set22; a third planetary gear set24and a fourth planetary gear set26. In certain exemplary embodiments, as shown inFIG. 1, third and fourth planetary gear sets24,26may be a Simpson planetary gear set, e.g., such that third and fourth planetary gear sets24,26share a joint sun gear or sun gears of third and fourth planetary gear sets24,26are coupled or fixed together. The sun gear of second planetary gear set22may also constitute the ring gear of first planetary gear set20, and planet gears of first and second planetary gear sets20,22may be mounted to a joint planet carrier that is also coupled or fixedly connected to the ring gear of third planetary gear set24. The planet carrier of third planetary gear set24may also be coupled or fixedly connected to the ring gear of fourth planetary gear set26.

As may be seen inFIG. 1, automatic transmission10further includes a plurality of shifting elements. In particular, automatic transmission10includes a plurality of non-positive shift elements and at least one positive shifting element. The non-positive shift elements may be any suitable type of non-positive shift elements. For example, the non-positive shift elements may be multidisc friction shift elements or friction bands. In the exemplary embodiment ofFIG. 1, the non-positive shifting elements includes a multidisc clutch B, a multidisc brake C, a multidisc brake D and a multidisc clutch E. The positive shifting elements may also be any suitable type of positive shifting elements, e.g., that provide a form fit or torque proof connection. For example, the positive shifting elements may be dog clutches, dog brakes or claw clutches. In the exemplary embodiment ofFIG. 1, the at least one positive shifting element includes a dog clutch A and a dog clutch or brake F. As used herein, the term “clutch” may refer to mechanism for coupling or connecting two rotating components and the term “brake” may refer to a mechanism for coupling or connecting a rotating component to a non-rotating or static component.

The shifting elements of automatic transmission10selectively adjust between an open or disengaged configuration and a closed or engaged configuration. In the disengaged configuration, the shifting elements do not engage an associated component of the four planetary gear sets, e.g., and do not or negligibly interfere with rotation of the associated component of the four planetary gear sets relative to the shifting elements. Conversely, in the engaged configuration, the shifting elements engage the associated component of the four planetary gear sets, e.g., and hinder or prevent rotation of the associated component of the four planetary gear sets relative to the shifting elements. As may be seen inFIG. 1, dog clutch A selectively connects or couples input shaft12to the sun gear of second planetary gear set22and the ring gear of first planetary gear set20. Multidisc clutch B selectively connects or couples input shaft12to the sun gear of first planetary gear set20. Multidisc brake C selectively connects or couples a transmission housing16to the sun gear of first planetary gear set20. Multidisc brake D selectively connects or couples transmission housing16to the ring gear of second planetary gear set22. Multidisc clutch E selectively connects or couples input shaft12to the planet carrier of third planetary gear set24and the ring gear of fourth planetary gear set26. Dog clutch F selectively connects or couples transmission housing16to the sun gear of third and fourth planetary gear sets24,26.

Automatic transmission10also includes an electronic control unit28, an input speed sensor30and an output speed sensor32. Electronic control unit28is in operative communication with various components of automatic transmission10, including input speed sensor30and output speed sensor32, to regulate operation of automatic transmission10. Electronic control unit28may include a memory and microprocessor, such as a general or special purpose microprocessor operable to execute programming instructions or micro-control code associated with operating of automatic transmission10. The memory may represent random access memory such as DRAM, or read only memory such as ROM or FLASH. Alternatively, electronic control unit28may be constructed without using a microprocessor, e.g., using a combination of discrete analog and/or digital logic circuitry (such as switches, amplifiers, integrators, comparators, flip-flops, AND gates, and the like) to perform control functionality instead of relying upon software.

Electronic control unit28may be mounted on an exterior of transmission housing16. Electronic control unit28is in operative communication with solenoid valves of the shifting elements of automatic transmission10. Thus, electronic control unit28may selectively adjust the shifting elements between the engaged configuration and the disengaged configuration, e.g., by selectively opening and closing the associated solenoid valves of the shifting elements. In such a manner, electronic control unit28may shift automatic transmission10between gears during operation of automatic transmission10, e.g., based at least in part on signals from input speed sensor30and output speed sensor32, as will be understood by those skilled in the art.

Input speed sensor30is configured for measuring a speed, e.g., rotations per minute (RPM), of input shaft12. Input speed sensor30may be positioned adjacent input shaft12or a turbine of an associated torque coupling. Input speed sensor30may be any suitable type of sensor. For example, input speed sensor30may be a Hall effect sensor, an optical sensor, etc. Electronic control unit28may receive a signal from input speed sensor30corresponding to the speed of input shaft12.

Output speed sensor32is configured for measuring a speed, e.g., rotations per minute (RPM), of output shaft14. Output speed sensor32may be positioned adjacent output shaft14. Output speed sensor32may be any suitable type of sensor. For example, output speed sensor32may be a Hall effect sensor, an optical sensor, etc. Electronic control unit28may receive a signal from output speed sensor32corresponding to the speed of output shaft14.

FIG. 2illustrates a table200of an exemplary shifting scheme as may be used with automatic transmission10. As may be seen inFIG. 2, automatic transmission10includes nine forward gears and one reverse gear. The forwards gears include: first gear “1”, second gear “2”, third gear “3”, fourth gear “4”, fifth gear “5”, sixth gear “6”, seventh gear “7”, eighth gear “8”, and ninth gear “9”. The reverse gear is labeled “R”. In table200, cells filled with “x” indicate the engaged configuration, and blank cells indicate the disengaged configuration. Thus, e.g., dog clutch A, multidisc brake D and dog clutch F are in the engaged configuration in first gear, and multidisc clutch B, multidisc brake C and multidisc clutch E are in the disengaged configuration in first gear. As another example, dog clutch A, multidisc brake C and dog clutch F are in the engaged configuration in second gear, and multidisc clutch B, multidisc brake D and multidisc clutch E are in the disengaged configuration in second gear. In the fourth gear, dog clutch A, multidisc clutch E and dog clutch F are in the engaged configuration. It should be understood that in certain exemplary embodiments, dog clutch A need not be in the engaged configuration to operate automatic transmission10in fourth gear. Thus, multidisc clutch E and dog clutch F may be the only shifting elements of automatic transmission10in the engaged configuration to operate automatic transmission10in fourth gear, in certain exemplary embodiments.

As discussed above, automatic transmission10includes nine forward gears and one reverse gear. Thus, automatic transmission10is generally referred to as a “nine-speed automatic transmission.” However, it should be understood that automatic transmission10is provided by way of example only and that the present subject matter may be used in or with any suitable automatic transmission. Thus, the present subject matter is not intended to be limited to use with automatic transmission10. As an example, the present subject matter may be used in automatic transmissions having five forward gears, six forward gears, eight forward gears, etc.

FIGS. 3 and 4provide section views of a dog clutch300according to an exemplary embodiment of the present subject matter with dog clutch300shown in various positions. InFIG. 3, dog clutch300is shown in a disengaged configuration. Conversely, dog clutch300is shown in an engaged configuration inFIG. 4. Dog clutch300may be used in any suitable automatic transmission. For example, dog clutch300may be used in automatic transmission10as dog clutch A and/or dog clutch F (FIG. 1). Thus, while described in greater detail below in the context of automatic transmission10, it will be understood that dog clutch300may be used in or with any other suitable transmission, such as a six-speed automatic transmission, an eight-speed automatic transmission, a ten-speed automatic transmission, etc., in alternative exemplary embodiments. As discussed in greater detail below, dog clutch300includes features for assisting with shifting dog clutch300between the engaged configuration and the disengaged configuration, e.g., without using hydraulic fluid.

As may be seen inFIGS. 3 and 4, dog clutch300includes a clutch support310, a sliding clutch320and a mating clutch330. Clutch support310may be mounted or fixed to any suitable component of automatic transmission10, e.g., such that clutch support310does not rotate relative to such component. For example, clutch support310may be mounted or fixed to input shaft12when used as dog clutch A or to transmission housing16when used as dog clutch F. Mating clutch330may also be mounted or fixed to any suitable component of automatic transmission10, e.g., such that mating clutch330does not rotate relative to such component. For example, mating clutch330may be mounted or fixed to the sun gear of second planetary gear set22and the ring gear of first planetary gear set20when used as dog clutch A or to the sun gear of third and fourth planetary gear sets24,26when used as dog clutch F.

As discussed above, dog clutch300is adjustable between an engaged configuration and a disengaged configuration. In the engaged configuration, sliding clutch320engages mating clutch330, e.g., such that clutch support310and mating clutch330rotate at a common angular velocity about an axis of rotation R. Conversely, in the disengaged configuration, sliding clutch320does not engage mating clutch330, e.g., such that clutch support310and mating clutch330may rotate relative to each other about the axis of rotation R. As discussed in greater detail below, sliding clutch320is configured for moving axially, e.g., along the axis of rotation R, in order to shift dog clutch300between the engaged and disengaged configurations.

Clutch support310defines a plurality of projections or splines312. Splines312of clutch support310may be positioned on or at an inner surface314of clutch support310. Splines312of clutch support310may be milled, broached or otherwise suitably formed on inner surface314of clutch support310. Splines312of clutch support310may also extend axially along the inner surface314of clutch support310and also radially inward from inner surface314of clutch support310, as shown inFIG. 3. In particular, clutch support310defines an interior chamber354. Inner surface314of clutch support310faces or is positioned adjacent interior chamber354of clutch support310, and splines312of clutch support310extend radially inward from inner surface314of clutch support310into interior chamber354of clutch support310. Clutch support310may have a generally cylindrical shape with a base plate318mounted thereto.

Mating clutch330also defines a plurality of projections or splines332. Splines332of mating clutch330may be positioned on or at an outer surface334of mating clutch330. Splines332of mating clutch330may be milled, broached or otherwise suitably formed on outer surface334of mating clutch330. Splines332of mating clutch330may also extend axially along the outer surface334of mating clutch330and also radially outward from outer surface334of mating clutch330, as shown inFIG. 3. Mating clutch330may have a generally cylindrical shape.

Sliding clutch320defines a first plurality of projections or splines322and a second plurality of projections or splines326. First splines322of sliding clutch320may be positioned on or at an inner surface324of sliding clutch320. First splines322of sliding clutch320may be milled, shaped, extruded or otherwise suitably formed on inner surface324of sliding clutch320. First splines322of sliding clutch320may also extend axially along the inner surface324of sliding clutch320and also radially inward from inner surface324of sliding clutch320, as shown inFIG. 3. The number and/or sizing of first splines322of sliding clutch320may correspond to or match the number and/or sizing of splines332of mating clutch330. Thus, first splines322of sliding clutch320may mesh with splines332of mating clutch330, as discussed in greater detail below. First splines322of sliding clutch320may also be uniformly distributed or spaced apart from one another on inner surface324of sliding clutch320.

Second splines326of sliding clutch320may be positioned on or at an outer surface328of sliding clutch320. Thus, second splines326of sliding clutch320may be positioned opposite first splines322of sliding clutch320on sliding clutch320. Second splines326of sliding clutch320may be milled, shaped, extruded or otherwise suitably formed on outer surface328of sliding clutch320. Second splines326of sliding clutch320may also extend axially along the outer surface328of sliding clutch320and also radially outward from outer surface328of sliding clutch320, as shown inFIG. 3. The number and/or sizing of second splines326of sliding clutch320may correspond to or match the number and/or sizing of splines312of clutch support310. Thus, second splines326of sliding clutch320may mesh with splines312of clutch support310in order to hinder rotation of sliding clutch320relative to clutch support310while permitting translation of sliding clutch320relative to clutch support310, e.g., along the axis or rotation R. Second splines326of sliding clutch320may mesh with splines312of clutch support310in both the engaged and disengaged configurations. Second splines326of sliding clutch320may also be uniformly distributed or spaced apart from one another on outer surface328of sliding clutch320.

Dog clutch300also includes a shape-memory alloy shifter340. Shape-memory alloy shifter340is positioned adjacent sliding clutch320and is configured for selectively adjusting dog clutch300between the engaged configuration and the disengaged configuration. For example, an electrical current may be supplied to shape-memory alloy shifter340, and shape-memory alloy shifter340may expand in order to move sliding clutch320relative to mating clutch330. The electrical current to shape-memory alloy shifter340may be subsequently terminated, and shape-memory alloy shifter340may contract in order to move sliding clutch320relative to mating clutch330. Such movement of sliding clutch320selectively engages first splines322of sliding clutch320with splines332of mating clutch330in order to shift dog clutch300between the engaged and disengaged configurations. In particular, shape-memory alloy shifter340positions sliding clutch320such that first splines322of sliding clutch320mesh with splines332of mating clutch330in the engaged configuration. Conversely, shape-memory alloy shifter340positions sliding clutch320such that first splines322of sliding clutch320do not mesh with splines332of mating clutch330in the disengaged configuration. Shape-memory alloy shifter340may be positioned within interior chamber354of clutch support310.

Shape-memory alloy shifter340may have any suitable shape. For example, as shown inFIGS. 3 and 4, shape-memory alloy shifter340may have a helical coil shape and extend between clutch support310and sliding clutch320within clutch support310. In particular, shape-memory alloy shifter340may extend between a first end portion342and a second end portion344, e.g., along the axis of rotation R. Shape-memory alloy shifter340may be mounted or fixed to clutch support310at or adjacent first end portion342of shape-memory alloy shifter340, and shape-memory alloy shifter340may be mounted or fixed to sliding clutch320at or adjacent second end portion344of shape-memory alloy shifter340. When shape-memory alloy shifter340has a helical coil shape, shape-memory alloy shifter340may apply a uniform or constant force to sliding clutch320during shifting between the engaged and disengaged configurations in order to assist with smoothly shifting dog clutch300between the engaged and disengaged configurations. In addition, shape-memory alloy shifter340may be completely compressed in the disengaged configuration when shape-memory alloy shifter340has a helical coil shape.

Clutch support310also extends between a first end portion350and a second end portion352, e.g., along the axis of rotation. Interior chamber354may extend, e.g., along the axis of rotation R, from first end portion350of clutch support310to second end portion352of clutch support310. A cylindrical bearing bracket316of clutch support310is positioned within interior chamber354of clutch support310at or adjacent first end portion350of clutch support310, and sliding clutch320may be, e.g., at least partially, positioned within interior chamber354of clutch support310at or adjacent second end portion352of clutch support310. Shape-memory alloy shifter340may be disposed within cylindrical bearing bracket316of clutch support310, e.g., at or adjacent first end portion350of clutch support310.

Dog clutch300also includes a controller370, such as electronic control unit28, and a power supply372, such as an alternator or battery, for regulating operation of shape-memory alloy shifter340. Controller370and power supply372are shown schematically inFIGS. 3 and 4. Power supply372is electrically coupled to shape-memory alloy shifter340, e.g., via suitable wiring, such that power supply372selectively directs an electrical current to shape-memory alloy shifter340. Controller370is in operative communication with power supply372such that controller370selectively operates power supply372in order to supply the electrical current to shape-memory alloy shifter340. Controller370may also regulate the magnitude of the electrical current from power supply372to shape-memory alloy shifter340.

Controller370is configured for selectively actuating power supply372in order to adjust dog clutch300between the engaged and disengaged configurations. For example, controller370may direct power supply372to direct an electrical current to shape-memory alloy shifter340in order to extend sliding clutch320towards mating clutch330and shift dog clutch300to the engaged configuration, as shown inFIG. 4. As another example, controller370may deactivate power supply372in order to terminate the electrical current to shape-memory alloy shifter340and retract sliding clutch320from mating clutch330such that dog clutch300shifts to the disengaged configuration, as shown inFIG. 3. Thus, controller370may adjust dog clutch300between the engaged and disengaged configurations by selectively directing electrical current from power supply372to shape-memory alloy shifter340.