Efficient eight speed automatic transmission

The present invention provides an eight speed automatic transmission for motor vehicles having three planetary gear sets, four friction clutches, a friction brake, a band brake and an optional overrunning clutch. The eight speed transmission according to the present invention exhibits good gear ratio progression and high efficiency due to its excellent gear mesh efficiency, low spin losses and low pinion speeds.

FIELD

The present disclosure relates to an automatic transmission and more particularly to a high efficiency eight speed automatic transmission for motor vehicles.

BACKGROUND

A typical modern multiple speed automatic transmission includes a combination of planetary gear assemblies and selectively engaged clutches which achieve a plurality of forward speeds or gears ratios and reverse.

Whereas three and four speed automatic transmissions were once commonplace, considered suitable and provided sufficient flexibility and performance, the industry and consumer preference is moving to six, seven and eight speed automatic transmissions.

In such transmissions, various elements of a plurality of planetary gear assemblies are connected by permanent couplings, selectively connected by clutches and selectively grounded by brakes. Specific combinations of the clutches and brakes are engaged or activated to provide a sequence of numerically related gear ratios and thus speed and torque ratios.

Because they so closely match the power and torque curves of the engine to the imposed load and speed of the vehicle, such six, seven and eight speed transmissions provide significant performance enhancements and reduced fuel consumption.

The present invention is directed to an eight speed automatic transmission having a good ratio progression, excellent gear mesh efficiency, low spin losses and low pinion speeds.

SUMMARY

The present invention provides an eight speed automatic transmission for motor vehicles having three planetary gear sets, four friction clutches, a friction brake and a band brake. The eight speed transmission according to the present invention exhibits high efficiency due to its excellent gear mesh efficiency, low spin losses and low pinion speeds. To improve the quality of the first gear to second gear shift, a freewheeling or overrunning clutch may also be included in the transmission.

Thus it is an object of the present invention to provide an eight speed automatic transmission.

It is a further object of the present invention to provide a high efficiency eight speed automatic transmission.

It is a still further object of the present invention to provide a high efficiency eight speed automatic transmission having a plurality of planetary gear assemblies, friction clutches and brakes.

It is a still further object of the present invention to provide a high efficiency eight speed automatic transmission having three planetary gear assemblies, four friction clutches, a friction brake and a band brake.

It is a still further object of the present invention to provide a high efficiency eight speed automatic transmission having three planetary gear assemblies, four friction clutches, a friction brake, a band brake and, optionally, a one way or overrunning clutch.

It is a still further object of the present invention to provide an eight speed automatic transmission having good gear mesh efficiency, low spin losses and low pinion speeds.

DETAILED DESCRIPTION

With reference now toFIG. 1, a multiple, i.e., eight, speed automatic transmission10according to the present invention is illustrated in a lever diagram. A lever diagram is a schematic representation of the components of an automatic transmission wherein components of planetary gear assemblies are represented by nodes and the planetary gear assemblies themselves are represented by bold vertical bars. The relative lengths of the vertical bars between nodes of a given planetary gear assembly represent the ratios between the components. Mechanical couplings or interconnections between the nodes of various planetary gear assemblies are represented by horizontal lines and torque transmitting devices such as friction clutches and brakes are represented by interleaved or nested fingers. Further explanation of the format, purpose and use of lever diagrams can be found in SAE Paper No. 810102 entitled “The Lever Analogy: A New Tool in Transmission Analysis” by Benford and Leising which is fully incorporated herein by reference.

The multiple speed automatic transmission10includes an input shaft or member12which is driven by the output of a torque converter (not illustrated), a first planetary gear assembly14having three nodes: a first node14A, a second node14B and a third node14C; a second planetary gear assembly16having three nodes: a first node16A, a second node16B and a third node16C and a third planetary gear assembly18having a first node18A, a second node18B and third node18C. Drive torque from the transmission10is delivered by an output shaft or member20to a final drive assembly (not illustrated).

The first node18A of the third planetary gear assembly18is coupled to and driven by the input shaft12. The third node14C of the first planetary gear assembly14is coupled to the first node16A of the second planetary gear assembly16. The first node14A of the first planetary gear assembly14is coupled to ground such as a housing22of the transmission10. The third node16C if the second planetary gear assembly16is coupled to and drives the output shaft20.

It should be noted that the inventor is familiar with the convention of characterizing a torque controlling or selectively transmitting device disposed between two rotatable members as a clutch whereas such a device disposed between one rotatable member and one fixed or stationary member is characterized as a brake. Within the transmission art, however, such torque controlling or transmitting devices are collectively referred to or characterized as clutches. Accordingly, in the following description, such devices will be referred to or characterized as clutches and if their application and use involves a stationary member to which a rotating member is selectively connected and grounded, the word “brake” will appear in parentheses following the word “clutch.”

A first friction clutch (brake)30selectively connects the third node18C of the third planetary gear set18to ground such as the transmission housing22. A second friction clutch32selectively connects the second node14B of the first planetary gear assembly14to the third node18C of the third planetary gear assembly18. A third friction clutch34selectively connects the third node14C of the first planetary gear assembly14to the second node18B of the third planetary gear assembly18. A fourth friction clutch36selectively connects the second node16B of the second planetary gear assembly16to the second node18B of the third planetary gear assembly18. A fifth friction clutch38selectively connects the second node16B of the second planetary gear assembly16to the first node18A of the third planetary gear assembly18. A first band clutch (brake)40selectively connects the second node16B of the second planetary gear assembly16to ground such as the transmission housing22.

An optional first freewheeling or overrunning clutch (brake)42couples the second node16B of the second planetary gear assembly16to ground such as the transmission housing22upon rotation relative to ground in one direction and allows the second node16B of the second planetary gear assembly16to freewheel or overrun upon rotation relative to ground, i.e., the transmission housing22, in the opposite direction.

Referring now toFIG. 2, a stick diagram presents a schematic layout of the eight speed automatic transmission10according to the present invention. InFIG. 2, the numbering from the lever diagram ofFIG. 1has been carried over. Thus, the clutches, brakes and couplings are correspondingly presented whereas the nodes of the planetary gear assemblies now appear as components of planetary gear assemblies such as sun gears, planet gear carriers and ring gears.

The input shaft or member12is continuously connected to and driven by a turbine of a torque converter (not illustrated) which, in turn, is driven by the output of an engine (also not illustrated). The input shaft12or an extension thereof is coupled to a third sun gear18A of the third simple planetary gear assembly18and one side of the fifth friction clutch38. A first shaft, quill or intermediate member50couples a third ring gear18C of the third simple planetary gear assembly18and the ungrounded side of the first friction clutch (brake)30to one side of the second friction clutch32. The other side of the second friction clutch32is coupled by a second shaft, quill or intermediate member52to a first planet gear carrier14B of the first simple planetary gear assembly14. Rotatably disposed in the first planet gear carrier14B of the first simple planetary gear assembly14are a plurality of first planet gears14D, one of which is illustrated inFIG. 2, which are in constant mesh with the first sun gear14A and the first ring gear14C of the first simple planetary gear assembly14. A third shaft, quill or intermediate member54couples the third planet gear carrier18B of the third simple planetary gear assembly18to one side of the third friction clutch34and one side of the fourth friction clutch36. Rotatably disposed in the third planet gear carrier18B of the third simple planetary gear assembly18are a third plurality of planet gears18D, one of which is illustrated inFIG. 2, which are in constant mesh with the third sun gear18A and the third ring gear18C of the third simple planetary gear assembly18.

A fourth shaft, quill or intermediate member56couples the other side of the third friction clutch34to a first ring gear14C of the first simple planetary gear assembly14and a second sun gear16A of the second simple planetary gear assembly16. A fifth shaft, quill or intermediate member58couples the other side of the fourth friction clutch36and the other side of the fifth friction clutch38to a second planet gear carrier16B of the second simple planetary gear assembly16. Rotatably disposed in the second planet gear carrier16B of the second simple planetary gear assembly16are a plurality of second planet gears16D, one of which is illustrated inFIG. 2, which are in constant mesh with the second sun gear16A and a second ring gear16C of the second simple planetary gear assembly16.

A sixth shaft, quill or intermediate member60couples a first sun gear14A of the first simple planetary gear assembly14and one side of the optional first freewheeling or overrunning clutch (brake)42to ground, such as the housing22of the automatic transmission10. It should be understood that the first freewheeling or overrunning clutch (brake)42is optional and may be included in the automatic transmission10when the smoothest possible shift between first and second gears is desired. A seventh shaft, quill or intermediate member62couples the second planet gear carrier16B of the second simple planetary gear assembly16(and the fourth and fifth friction clutches36and38through the fifth shaft, quill or intermediate member58) and the other side of the first freewheeling or overrunning clutch (brake)42with one side of the first band clutch (brake)40. The other side of the first band clutch (brake)40is coupled to ground such as the housing22of the automatic transmission10. The output shaft or member20is coupled to and driven by the second ring gear16C of the second planetary gear assembly16and, as noted above, is coupled to and drives a final drive assembly such as a prop shaft, differential and axles (all not illustrated).

Referring now toFIG. 3, a truth table is presented which sets forth the various combinations of torque transmitting devices, i.e., clutches and brakes, that are engaged or activated to achieve the various forward and reverse gear states or ratios. Actual numerical gear ratios of the various gear states are also presented although it should be appreciated that these numerical gear ratios are presented by way of illustration and example only and that they may be adjusted over significant ranges to accommodate various applications and operational criteria of the automatic transmission10.

In the truth table ofFIG. 3, an “X” means a torque transmitting device is activated or engaged and is carrying torque, an “O” means a torque transmitting device is activated or engaged but is not carrying torque, a “G” means the torque transmitting device is a garage shift element, is activated or engaged and is carrying torque and a “C” means a torque transmitting device is activated or engaged only in a manual range or setting of the automatic transmission10for coast (engine) braking.

In reverse gear, the second friction clutch32and the first band clutch (brake)40are engaged or activated and the third friction clutch34is engaged or activated as a garage shift element and is also carrying torque.

In neutral, both the second friction clutch32and the first band clutch (brake)40are engaged or activated but neither is carrying torque.

In first gear, the second friction clutch32is engaged or activated, the fourth friction clutch36is engaged or activated as a garage shift element and the first freewheeling or overrunning clutch (brake)42is engaged (locked) and connects the seventh shaft, quill or intermediate member62, the second planet gear carrier16B of the second simple planetary gear assembly16and associated components to ground. Additionally, the first band clutch (brake)40may be engaged or activated in the manual range for coast (engine) braking, if desired.

In second gear, if it is achieved in direct sequence from or following first gear, the first band clutch (brake)40, if engaged in first gear, is disengaged or deactivated and the first freewheeling or overrunning clutch (brake)42is released or disengaged due to a change in the relative direction of rotation between the elements. As noted above, the first freewheeling or overrunning clutch (brake)42is an optional component in the automatic transmission10which is utilized to improve the quality of the first to second gear shift. The second friction clutch32and the fourth friction clutch36are maintained in their activated or engaged states and the first friction clutch (brake)30is activated or engaged.

In third gear, if it is achieved in direct sequence from or following second gear, the second friction clutch32and the fourth friction clutch36are maintained in their activated or engaged states, the first friction clutch (brake)30is deactivated or disengaged and the third friction clutch34is activated or engaged.

In fourth gear, if it is achieved in direct sequence from or following third gear, the second friction clutch32and the fourth friction clutch36are maintained in their activated or engaged states, the third friction clutch34is deactivated or disengaged and the fifth friction clutch38is activated or engaged.

In fifth gear, if it is achieved in direct sequence from or following fourth gear, the fourth friction clutch36and the fifth friction clutch38are maintained in their activated or engaged states, the second friction clutch32is deactivated or disengaged and the third friction clutch34is activated or engaged.

Sixth, seventh and eighth gears are achieved in a similar manner according to the activation or engagement sequence and states set forth inFIG. 3.

With regard to the foregoing described operation, several features and operational considerations should be noted. First of all, the incorporation of the first freewheeling or overrunning clutch (brake)42provides significantly improved first to second gear shifts, especially during hard acceleration. Without the freewheeling clutch42, the smoothness of the first to second gear shift is primarily dependent upon simultaneous release of one clutch and engagement of another which can be an engineering and operational challenge. The freewheeling clutch42obviates this situation by simply releasing certain elements when a desired relative rotational condition is achieved. Second of all, the foregoing description assumes that all clutches and brakes not specifically referenced in a given gear state are inactive or disengaged. Furthermore, and as noted, the description also assumes that during gear shifts between at least adjacent gear states, a clutch or brake that is activated or engaged in both gear states will remain activated or engaged during the shift. Finally, the foregoing description assumes that downshifts follow essentially the opposite sequence of shifts and that power on skip shifts, e.g., from first to third gear or eight to sixth gear, are possible.