Abstract:
A multi-speed transmission is provided with a selectable (reversible) braking one-way clutch operative to brake rotation of a member of a planetary gear set of the transmission when the transmission is in reverse and first speed. First and second rotating input clutches are slipped when the vehicle is launched in reverse or first speed. The transmission is preferably characterized by the absence of a torque converter, but the invention may be implemented with a torque converter if desired.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to a transmission having a selectable braking one-way clutch which is engaged in first and reverse speeds, and having rotating input clutches that are slipped for launch in forward and reverse.  
       BACKGROUND OF THE INVENTION  
       [0002]     Vehicle powertrains typically include a torque converter positioned between the engine and the transmission. The torque converter is a fluid coupling which allows the engine to spin while the vehicle wheels and transmission gears come to a stop. If the engine is rotating slowly, such as when the car is idling at a stop light, the amount of torque passed through the torque converter is very small, so the car may be kept still with light pressure on a brake pedal. As the engine accelerates, the torque converter pumps increased amounts of fluid, thereby causing increased amounts of torque to be transmitted to the wheels for launching the vehicle.  
         [0003]     Manual transmission vehicles use a clutch, which completely disconnects the engine from the transmission, to allow the engine to run while the vehicle wheels and transmission gears are at rest. In order to launch the vehicle, the clutch is slipped and gradually engaged to connect the rotating engine output with the transmission input, thereby moving the wheels and launching the vehicle.  
         [0004]     Automatic transmissions sometimes eliminate the torque converter and replace it with a flywheel and isolator to achieve a friction launch configuration. In a friction launch configuration, one or more clutches inside the transmission are slipped and gradually engaged to gradually transfer torque from the engine into the transmission for launch.  
         [0005]     Some automatic transmissions include a low/reverse braking clutch and a freewheeler to provide reaction torque in both forward and reverse directions as input clutches are slipped for launching the vehicle without a torque converter.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention provides a transmission having a selectable braking freewheeler engaged in first and reverse speeds, and rotating input clutches that are slipped for launch in the forward and reverse speeds. This configuration eliminates the prior art low/reverse braking clutch and freewheeler, thereby improving transmission costs, packaging, and mass. This configuration is particularly useful in a friction launch configuration, but benefits of the invention are also achieved when the configuration of the present invention is used with a torque converter.  
         [0007]     More specifically, the invention provides a multi-speed transmission for a vehicle including an input shaft, an output shaft, and a plurality of planetary gear sets operatively connected between the input shaft and the output shaft. Each planetary gear set includes a ring gear member, a planet carrier assembly member, and a sun gear member. A selectable braking one-way clutch is operative to brake rotation of one of the members of the planetary gear sets when the transmission is in reverse and first speed. A first rotating input clutch is operatively engageable with the input shaft, and is slipped for launching the vehicle in first speed when the invention is implemented without a torque converter. A second rotating input clutch is operatively engageable with the input shaft, and is slipped for launching the vehicle in reverse.  
         [0008]     The selectable braking one-way clutch is a reversible one-way clutch which is connected to the transmission housing. The selectable braking one-way clutch may be a selectable diode or a selectable roller clutch.  
         [0009]     The selectable braking one-way clutch is actuated hydraulically by a piston and valve. The selectable braking one-way clutch is configured to freewheel in one rotational direction and to brake in an opposite rotational direction, and is selectably reversible to brake in said one rotational direction and freewheel in said opposite rotational direction, thereby facilitating use in the reverse and forward speeds.  
         [0010]     The selectable braking one-way clutch is preferably connected between the planet carrier assembly member of the second planetary gear set and a transmission housing.  
         [0011]     The first and second rotating input clutches are operatively engageable with the input shaft through one of the members of the planetary gear sets. Preferably, the input shaft is connected to a member of one of the planetary gear sets, and the first and second rotating input clutches are connected to another member of the planetary gear set to which the input shaft is connected. Preferably, the input shaft is connected to the ring gear member of the first planetary gear set, and the first and second rotating input clutches are connected to the planet carrier assembly member of the first planetary gear set.  
         [0012]     A third clutch and a brake may also be provided. The first, second and third clutches, the brake, and the selectable braking one-way clutch may be engageable in combinations of two to provide six forward speed ratios and one reverse speed ratio between the input shaft and the output shaft.  
         [0013]     The input shaft is preferably connected to the ring gear member of the first planetary gear set, and the output shaft is connected to the ring gear member of the third planetary gear set. The first clutch is operatively connected between the planet carrier assembly member of the first planetary gear set and the sun gear member of the third planetary gear set. The second clutch is operatively connected between the planet carrier assembly member of the first planetary gear set and the sun gear member of the second planet carrier assembly member. The third clutch is operatively connected between the ring gear member of the first planetary gear set and the planet carrier assembly member of the third planetary gear set. The brake is operatively connected between the transmission housing and the sun gear member of the first planetary gear set. The selectable braking one-way clutch is operatively between the planet carrier assembly member of the second planetary gear set and the transmission housing.  
         [0014]     Again, the invention may be characterized by the absence of a torque converter, but the invention may be implemented with a torque converter, if desired.  
         [0015]     The above features and advantages, and other features and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  shows a stick diagram of a transmission in accordance with the invention;  
         [0017]      FIG. 2  shows a clutching table for use with the transmission of  FIG. 1 ;  
         [0018]      FIG. 3  shows a schematic partial cross-sectional side view of a transmission corresponding with the stick diagram of  FIG. 1 ; and  
         [0019]      FIG. 4  shows a schematic vertical cross-sectional end view of a transmission incorporating a selectable braking one-way clutch, as shown in  FIG. 3 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     Referring to  FIG. 1 , a stick diagram of a powertrain  10  is shown in accordance with the invention. The powertrain includes an engine  12 , a planetary transmission  14 , and a conventional final drive mechanism  16 .  
         [0021]     The planetary transmission  14  includes an input shaft  17  continuously connected with the engine  12 , a planetary gear arrangement  18 , and a output shaft  19  continuously connected with the final drive mechanism  16 . A torque converter may be positioned between the engine  12  and the input shaft  17 . If no torque converter is present, then an isolator would be positioned between the engine  12  and the input shaft  17 . The planetary gear arrangement  18  includes three planetary gear sets  20 ,  30  and  40 .  
         [0022]     The first planetary gear set  20  includes a sun gear member  22 , a ring gear member  24 , and a planet carrier assembly member  26 . The planet carrier assembly member  26  includes a plurality of pinion gears  27  rotatably mounted on a carrier member  29  and disposed in meshing relationship with both the sun gear member  22  and the ring gear member  24 .  
         [0023]     The second planetary gear set  30  includes a sun gear member  32 , a ring gear member  34 , and a planet carrier assembly member  36 . The planet carrier assembly member  36  includes a plurality of pinion gears  37  rotatably mounted on a carrier member  39  and disposed in meshing relationship with both the sun gear member  32  and the ring member  34 .  
         [0024]     The third planetary gear set  40  includes a sun gear member  42 , a ring gear member  44 , and a planet carrier assembly member  46 . The planet carrier assembly member  46  includes a plurality of pinion gears  47 ,  48  rotatably mounted on a carrier member  49 . The pinion gears  47  are disposed in meshing relationship with the sun gear member  42 , and the pinion gears  48  are disposed in meshing relationship with the ring gear member  44 . The ring gear member  34  is integral with the ring gear member  44 . The third planetary gear set  40  is a compound planetary gear set.  
         [0025]     The planetary gear arrangement also includes five torque transmitting mechanisms  50 ,  52 ,  54 ,  56  and  58 . The torque transmitting mechanisms  50 ,  54 ,  56  are rotating type torque transmitting mechanisms, commonly termed clutches. The torque transmitting mechanism  52  is a stationary type torque transmitting mechanism, commonly termed brake or reaction clutch. The torque transmitting mechanism  58  is a selectable braking one-way clutch or diode.  
         [0026]     The input shaft  17  is continuously connected with the ring gear member  24 , and the output shaft  19  is continuously connected with the ring gear member  44 . The planet carrier assembly member  26  is selectively connectable with the sun gear member  42  through the clutch  50 . The sun gear member  32  is selectively connectable with the transmission housing  60  through the brake  52 . The planet carrier assembly member  26  is selectively connectable with the sun gear member  32  through the clutch  54 . The ring gear member  24  is selectively connectable with the planet carrier assembly member  46  through the clutch  56 . The planet carrier assembly member  36  is selectively connectable with the transmission housing  60  through the braking one-way clutch  58 .  
         [0027]     As shown in the truth table or clutching table of  FIG. 2 , the torque transmitting mechanisms  50 ,  52 ,  54 ,  56  and  58  are selectively engaged in combinations of two to provide six forward speed ratios and a reverse speed ratio between the input shaft  17  and the output shaft  19 .  
         [0028]     The reverse speed ratio is established with the engagement of the clutch  54  and mechanical diode  58 . The numerical value of the reverse speed ratio is 3.20. The clutch  54  is slipped for launching the vehicle in reverse.  
         [0029]     The first forward speed ratio is established with the engagement of the clutch  50  and the mechanical diode  58 . The numerical value of the first forward speed ratio is 4.06. The clutch  50  is slipped for launching the vehicle in the forward direction.  
         [0030]     The second forward speed ratio is established with the engagement of the clutch  50  and the brake  52 . The numerical value of the second forward speed ratio is 2.37.  
         [0031]     The third forward speed ratio is established with the engagement of the brakes  50 ,  54 . The numerical value of the third forward speed ratio is 1.55.  
         [0032]     The fourth forward speed ratio is established with the engagement of the clutches  50 ,  56 . The numerical value of the fourth forward speed ratio is 1.16.  
         [0033]     The fifth forward speed ratio is established with the engagement of the clutches  54 ,  56 . The numerical value of the fifth forward speed ratio is 0.85.  
         [0034]     The sixth forward speed ratio is established with the engagement of the brake  52  and clutch  56 . The numerical value of the sixth forward speed ratio is 0.67.  
         [0035]     As set forth above, the engagement schedule or clutching schedule for the torque transmitting mechanisms is shown in the truth table of  FIG. 2 . Also, the chart of  FIG. 2  describes the ratio steps that are attained utilizing sample tooth ratios (not shown). For example, the step ratio between the first and second forward speed ratios is 1.71, while the step ratio between the reverse and first forward ratio is −0.79. It can also be readily determined from the truth table of  FIG. 2  that all of the single step forward ratio interchanges are of the single transition variety, as are the double step forward ratio interchanges.  
         [0036]     Referring to  FIG. 3 , a schematic partial cross-sectional view of a transmission  14  is shown corresponding with the stick diagram of  FIG. 1 . Like reference numerals are used to describe like components in the various figures.  
         [0037]     As shown, the transmission  14  includes a transmission housing  60  enclosing planetary gear sets  30 ,  40  which rotate about a shaft  17 . The position of the diode (selectable braking one-way clutch)  58  is shown in  FIG. 3 . The outer race  70  of the diode  58  is splined to the spline  72  on the transmission housing  60 . The inner race  74  of the diode  58  is splined to the planet carrier assembly member  36 . A snap ring  76  keeps the diode  58  in place.  
         [0038]     The diode  58  is a selectable braking one-way clutch, which may be a controllable overrunning coupling or a bi-directional differential clutch. A controllable overrunning coupling (or selectable diode) is shown in U.S. Pat. No. 6,244,965, which is hereby incorporated by reference herein. A bi-directional differential clutch (or selectable roller clutch) is shown in U.S. Pat. No. 5,025,902, which is hereby incorporated by reference herein. The invention contemplates that other selectable (reversible) one-way clutches could be used as defined herein with the present invention.  
         [0039]      FIG. 4  shows a schematic vertical cross-sectional view of the transmission  14  incorporating the mechanical diode  58 . This mechanical diode  58  may be identical in function to that described in U.S. Pat. No. 6,244,965, referenced above. As shown, this structure includes a grounding ring  80  which is connected to the transmission housing  60 , a one-way clutch outer  82 , a one-way clutch inner  84 , and a carrier  86 . The functionality of one-way clutches is described in detail in the above referenced patents. The selectable braking one-way clutch  58  is configured to freewheel in one rotational direction and to brake in an opposite rotational direction, and is selectively reversible to brake in said one rotational direction and freewheel in said opposite rotational direction, thereby facilitating use in the reverse and forward speeds.  
         [0040]     The selectable braking one-way clutch  58  is actuated hydraulically by a piston and valve assembly  90 . The piston and valve assembly  90  is positioned adjacent a valve body  92  and receives fluid from the valve body  92  into an apply chamber  94  through a channel  96  to actuate movement of the piston  98  against the spring  100 . Movement of the piston  98  to the right, as viewed in  FIG. 4 , pivots the lever  102  to the right, and movement of the piston  98  to the left pivots the lever  102  to the left. The lever is operative to reverse the freewheeling direction of the selectable braking one-way clutch  58  as it is pivoted between the left and right positions by the piston  98 .  
         [0041]     In operation, the lever  102  is pivoted to the right when the transmission is in reverse, and pivoted to the left when the transmission is in first speed. Accordingly, the fail safe mode is the first speed mode because the spring  100  biases the lever  102  toward the first speed position in the event of a system failure.  
         [0042]     Preferably, the piston and valve assembly  90  would be incorporated into the valve body  92  in a production configuration. The configuration shown in  FIG. 4  is merely a prototype.  
         [0043]     The lever  102  is connected to a selector plate which controls the selected rotational torque engagement direction of the diode  58 , as illustrated in the above-referenced patents. During all modes of operation except for reverse, the selector plate is in forward mode and in first gear the mechanical diode is holding the reaction torque. When the transmission shifts to second gear, the mechanical diode  58  will overrun, and thus the 1-2 shift becomes a freewheeler shift. The selector plate is also in forward mode with the transmission in neutral and park. When the transmission manual valve is moved from park, neutral or drive to reverse mode, the mechanical diode selector plate is moved into reverse position when the diode is unloaded. Because the diode  58  is connected to the transmission housing  60 , the diode  58  provides reaction torque in both forward and reverse directions as the input clutches  50  or  52  are slipped during launch.  
         [0044]     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.