Abstract:
An automatic transmission having an improved lock up torque converter configuration includes two drive members: a first quill or tubular drive member which carries the output of the torque converter to the transmission gearbox and a second co-axial shaft or drive member which is driven by the torque converter lockup clutch and thus directly carries the engine output to the transmission gear box and bypasses the torque converter. The transmission gearbox includes two planetary gear assemblies having certain elements which are selectively grounded to the transmission housing by two friction brakes. This transmission, torque converter and torque converter clutch configuration prevents torque converter clutch engagement in its lower gear and forces torque converter clutch lockup in its upper gear.

Description:
FIELD 
     The present disclosure relates to automatic transmissions for motor vehicles and more particularly to automatic transmissions having torque converter bypass in its upper gear or gears. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
     Design and development of automatic transmissions for motor vehicles is ongoing. Given the multiple goals of improved performance, improved fuel economy and reduced cost, nearly every aspect of automatic transmissions has been scrutinized, evaluated and re-evaluated. 
     One of the areas of focus is the torque converter and the torque converter clutch. In order to achieve disconnection between the engine and transmission when the vehicle is in gear and stopped and allow the engine to idle, in order to provide a smooth launch, and in order to increase low speed torque, a torque converter is disposed between the output of the engine and the input of the transmission. The hydrodynamic fluid coupling and torque multiplication provided thereby achieves and satisfies all the foregoing requirements. 
     Unfortunately, it does so in a somewhat expensive and inefficient manner. The frictional losses in a torque converter contribute to the reduced efficiency and fuel economy of an automatic transmission relative to a manual transmission. 
     One approach to improving the efficiency of a torque converter involves the addition of a torque converter clutch or “TCC,” a clutch in mechanical parallel with the torque converter which is engaged when the transmission reaches an upper gear (lower numerical ratio), thereby locking out the torque converter and avoiding or minimizing its inherent fluid and frictional losses. While the addition of a torque converter clutch has a significant impact on efficiency and fuel economy, it also increases the cost and complexity of the torque converter, the transmission and the powertrain. Hence, there is a desire to develop mechanical assemblies which, while providing the benefits of lock up torque converters, do so with reduced complexity and cost. 
     The present invention represents a further improvement relating to automatic transmissions and torque converter assemblies. 
     SUMMARY 
     The present invention provides an automatic transmission having an improved lock up torque converter configuration. The transmission/torque converter include two drive members: a first quill or tubular drive member which carries the output of the torque converter to the transmission gearbox and a second co-axial shaft or drive member which is driven by the torque converter lockup clutch and thus directly carries the engine output to the transmission gear box and bypasses the torque converter. This configuration, instead of achieving direct drive through the locked up torque converter, achieves it by bypassing the torque converter and transferring drive torque directly to the transmission gearbox in a separate shaft. The transmission gearbox includes two planetary gear assemblies having certain elements which are selectively grounded to the transmission housing by two friction brakes. This transmission, torque converter and torque converter clutch configuration prevents torque converter clutch engagement in lower gears and forces torque converter clutch lockup in upper gears. 
     It is thus an aspect of the present invention to provide an automatic transmission having an improved torque converter lockup clutch configuration. 
     It is a further aspect of the present invention to provide an automatic transmission having a shaft which extends through the torque converter to the transmission gearbox. 
     It is a still further aspect of the present invention to provide an automatic transmission having a quill which connects the torque converter output to the transmission gearbox and a shaft within the quill which connects the torque converter clutch output to the transmission gearbox. 
     It is a still further aspect of the present invention to provide an automatic transmission having a torque converter clutch which selectively connects the engine output to the transmission output shaft. 
     It is a still further aspect of the present invention to provide an automatic transmission having two planetary gear assemblies. 
     It is a still further aspect of the present invention to provide an automatic transmission having two selectively engageable friction brakes. 
     It is a still further aspect of the present invention to provide a torque converter clutch arrangement that prevents torque converter lockup in lower gears. 
     It is a still further aspect of the present invention to provide a torque converter clutch arrangement that forces torque converter lockup in upper gears. 
     Further aspects, advantages and areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a lever diagram of a two speed automatic transmission having a torque converter bypass according to the present invention; 
         FIG. 2  is a schematic diagram of a two speed automatic transmission having a torque converter bypass according to the present invention; and 
         FIG. 3  is a fragmentary, full sectional view of a two speed automatic transmission having a torque converter bypass according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
     With reference to  FIG. 1 , a two speed automatic transmission having torque converter bypass according to the present invention is illustrated in a lever diagram and is designated by the reference number  10 . A lever diagram is a schematic representation of the components of an automatic transmission wherein a planetary gear assembly is represented by a vertical bar or lever and the components of the planetary gear assemblies such as sun gears, planet gear carriers and ring gears are represented by nodes. The relative lengths of the vertical bars between the nodes represent the ratios between the components. Where, as here, there are only two planetary gear assemblies and a component of one planetary gear assembly is coupled directly to a component of another planetary gear assembly, the two levers are combined into a single lever having four nodes. 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 automatic transmission  10  includes an input shaft or member  12  which is coupled to and driven by the output of an internal combustion gas, Diesel or flex fuel engine or electric or hybrid power plant (not illustrated), an output shaft or member  14  which is coupled to and drives a final drive assembly (also not illustrated) which may include a prop shaft, a differential, axles and tires and wheels and a housing  16  which is referred to in  FIG. 1  as ground. The input shaft or member  12  is coupled to and drives an input of a torque converter  20  and also an input of a torque converter clutch (TCC)  40 . 
     The automatic transmission  10  also includes two planetary gear assemblies  50  and  70 . The first planetary gear assembly  50  includes a first node  50 A which is coupled to and driven by the output of the torque converter  20  and a second node  50 B which is coupled to and drives the output shaft or member  14 . There is no third node in the first planetary gear assembly  50 . The second planetary gear assembly  70  includes a first node  70 A, a second node  70 B which is common with the second node  50 B of the first planetary gear assembly  50  and which is coupled to and driven by the output of the torque converter clutch  40  and a third node  70 C. A first friction brake  90  is disposed between the first node  70 A of the second planetary gear assembly  70  and the transmission housing  16  (ground) and a second friction brake  100  is disposed between the third node  70 C of the second planetary gear assembly  70  and the transmission housing  16  (ground). 
     Referring now to  FIG. 2 , the automatic transmission  10  includes the input shaft or member  12  which is coupled to and drives the input of the torque converter clutch  40  and a pump  22  within the torque converter  20 . The torque converter  20  also includes a stator  24  which is connected through a one way or overrunning clutch  26  to the housing  16 . The torque converter  20  further includes a turbine  28  which is connected through a first drive member  30  such as a quill or tubular drive component to a first sun gear  52  of the first planetary gear assembly  50 . 
     The output of the torque converter clutch  40  is coupled through a second drive member  48  such as a shaft or quill to a planet gear carrier  54  common to both the first planetary gear assembly  50  and the second planetary gear assembly  70 . The planet gear carrier  54  is also coupled to and drives the output shaft or member  14 . The planet gear carrier  54  freely rotatably supports a plurality of first pinions or planet gears  56  that are typically disposed upon needle bearing assemblies supported on stub shafts (both not illustrated). The plurality of first pinions or planet gears  56  are in constant mesh with the first sun gear  52 . There is no ring gear in the first planetary gear assembly  50 . 
     Immediately adjacent the first planetary gear assembly  50  is a second planetary gear assembly  70 . The second planetary gear assembly  70  includes a second sun gear  72 , the planet gear carrier  54  which freely rotatably supports a plurality of second, elongate pinions or planet gears  76  that are typically disposed upon needle bearing assemblies supported on stub shafts (both not illustrated) and a second ring gear  78 . One end of each of the plurality of second, elongate pinions or planet gears  76 , the left ends in  FIGS. 2 and 3 , are in constant mesh with the second sun gear  72  and the second ring gear  78  and the other end of each of the plurality of second, elongate pinions or planet gears  76 , the right ends in  FIGS. 2 and 3 , are in constant mesh with the plurality of first pinion or planet gears  56 . 
     The first friction brake  90  is connected between the second sun gear  72  of the second planetary gear assembly  70  and the transmission housing  16  by a suitable first connecting member  92  and the second friction brake  100  is connected between the second ring gear  78  of the second planetary gear assembly  70  and the transmission housing  16  by an optional second connecting member  102 . 
     Referring now to  FIG. 3 , a fragmentary, full sectional view of the automatic transmission  10  illustrates the physical layout of the transmission and the torque converter bypass configuration. The input shaft or member  12  which may be the engine output shaft is coupled to a drive flange assembly  18  by suitable threaded fasteners  19  and may be piloted on the engine output shaft. The drive flange assembly  18  is connected to the pump  22  of the torque converter  20 . The stator  24  of the torque converter  20  is connected through the one way or overrunning clutch  26  to a stationary internal annular support  27  which is secured to the housing  16 . The turbine  28  of the torque converter  20  is connected through a first interengaging spline set  32  to the first drive member  30  which is a quill or similar tubular drive component which extends into the automatic transmission  10  proper, that is, the gearbox. 
     The torque converter lockup clutch  40  is disposed adjacent the drive flange assembly  18  which acts as a drive member therefor. Immediately adjacent the drive flange assembly  18  is a damper assembly  42  which includes a plurality of circumferentially oriented springs  44  and functions as the driven member of the torque converter lockup clutch  40 . An annulus of friction material  45  is secured to one of the opposing faces of the drive flange assembly  18  and the damper assembly  42  and functions as the frictional interface of the torque converter clutch  40 . The damper assembly  42  is piloted on, secured to and drives a damper hub  46 . The damper hub  46  is, in turn, disposed upon a second drive member  48  which may be a shaft or quill which extends into the transmission gearbox and is connected thereto by a second interengaging spline set  49 . The first drive member  30  and the second drive member  48  are co-axial. 
     Turning now to the first planetary gear assembly  50  and the second planetary gear assembly  70 , which generally constitute the gearbox of the automatic transmission  10 , the first drive member  30  includes a third interengaging spline set  58  which engages and drives the first sun gear  52 . The second drive member  48  includes lugs, teeth or male splines  79  which engage complementarily configured recesses, teeth or splines (not illustrated) in the planet gear carrier  54  (which is coupled to and drives the output member  14 ). 
     The second sun gear  72  is coupled through the first connecting member  92  to a first set of friction clutch plates of discs  94  of the first friction brake  90 . The first set of friction plates or discs  94  are interleaved with a second set of friction plates or discs  96  which are coupled to the housing  16 . A first clutch actuator  98  which may be hydraulically, electrically or pneumatically operated is disposed in operable relationship with the sets of friction plates or discs  94  and  96 . When the first actuator  98  is engaged or activated, the first friction brake  90  inhibits rotation of the second sun gear  72  by connecting it to the housing  16 . The second ring gear  78  is coupled through a fifth interengaging spline set  84  and the optional second connecting member  102  to a third set of friction clutch plates of discs  104  of the second friction brake  100 . The third set of friction plates or discs  104  are interleaved with a fourth set of friction plates or discs  106  which a coupled to the housing  16 . A clutch actuator  108  which may be hydraulically, electrically or pneumatically operated is disposed in operable relationship with the sets of friction plates or discs  104  and  106 . When the second actuator  108  is engaged or activated, the second friction brake  100  inhibits rotation of the second ring gear  78  by connecting it to the housing  16 . 
     The planet gear carrier  54  of the first planetary gear assembly  50  is coupled to a chain drive sprocket  110  by lugs, gear teeth or splines  112  which is piloted and supported on a roller bearing assembly  114 . The chain drive sprocket  110  engages a chain  116  which functions as the output member  14  and transfers drive torque to a final drive assembly (not illustrated). 
     It will be appreciated by those skilled in the transmission art that the automatic transmission  10  illustrated includes numerous features such as fasteners, seals, thrust and roller bearings and lubrication passageways and ports. Inasmuch as they are common and conventional features of such devices and form no inherent aspect of the present invention, they have not been not specifically identified as their incorporation and use are deemed to be understood. 
     Operation of the automatic transmission  10  will now be described briefly. Commencing from a stop, either the first friction brake  90  is engaged to achieve forward motion or the second friction brake is engaged to provide reverse. Assuming that the first friction brake  90  has been engaged, operation will commence in first gear, the speed of the output member  14  will increase and hydraulic pressure within the torque converter  20  and the torque converter lockup clutch  40  will increase. At a predetermined speed, the first friction brake  90  will be disengaged and the automatic transmission  10  will shift into the second of its two forward gears. Similarly, at a predetermined speed, the torque converter clutch  40  will lock up and provide direct drive from the input shaft  12 , through the second drive member  48  and to the output member  14 , such as the output chain  116 , the torque flow path completely bypassing the torque converter  20 . 
     The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.