Abstract:
A transmission includes an input member, an output member, four planetary gear sets, a plurality of coupling members and a plurality of torque transmitting devices. The transmission input member is connected to a dry launch clutch. Each of the planetary gear sets includes first, second and third members. The torque transmitting devices are for example clutches and brakes. A hill hold control strategy is provided for locking the transmission without using the dry launch clutch by selectively engaging combinations of the clutches and brakes.

Description:
CROSS-REFERENCE 
     This application claims the benefit of U.S. Provisional Application No. 61/430,505, filed Jan. 6, 2011. The entire contents of the above application are incorporated herein by reference. 
    
    
     FIELD 
     The invention relates generally to a torque transmitting device control strategy for a nine speed transmission having a plurality of planetary gear sets and a plurality of torque transmitting devices, and more particularly to a torque transmitting device control strategy for a nine speed transmission to implement a hill-hold clutch control strategy. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
     A typical multiple speed transmission uses a combination of friction clutches or brakes, planetary gear arrangements and fixed interconnections to achieve a plurality of gear ratios. The number and physical arrangement of the planetary gear sets, generally, are dictated by packaging, cost and desired speed ratios. 
     While current transmissions achieve their intended purpose, the need for new and improved transmission configurations which exhibit improved performance, especially from the standpoints of efficiency, responsiveness and smoothness and improved packaging, primarily reduced size and weight, is essentially constant. Accordingly, there is a need for an improved, cost-effective, compact multiple speed transmission. 
     SUMMARY 
     A transmission is provided having an input member, an output member, four planetary gear sets, a plurality of coupling members and a plurality of torque transmitting devices. The transmission input member is connected to a dry launch clutch. Each of the planetary gear sets includes first, second and third members. The torque transmitting devices are for example clutches and brakes. A hill hold control strategy is provided for locking the transmission without using the dry launch clutch by selectively engaging combinations of the clutches and brakes. 
     In one embodiment, a method for controlling a transmission in a motor vehicle includes providing a launch clutch and providing a transmission having an input member connected to the launch clutch, an output member, first, second, third, and fourth planetary gear sets each having a first, a second, and a third member, wherein the second member of the first planetary gear set is connected with the second member of the second planetary gear set, the third member of the first planetary gear set is connected with the third member of the second planetary gear set and the first member of the third planetary gear set, the second member of the third planetary gear set is connected with the second member of the fourth planetary gear set, and the third member of the third planetary gear set is connected with the third member of the fourth planetary gear set, and wherein a first clutch connects the first member of the second planetary gear set with the third members of the third and fourth planetary gear sets, a second clutch connects the first member of the second planetary gear set with the first member of the fourth planetary gear set, a first brake connects the first member of the first planetary gear set with a stationary member, a second brake connects the second members of the first and second planetary gear sets with the stationary member, a third brake connects the first member of the third planetary gear set and the third members of the first and second planetary gear sets with the stationary member, and a fourth brake connects the third members of the third and fourth planetary gear sets with the stationary member. Next the transmission is commanded into a Drive mode of operation and it is determined that the output shaft of the transmission should be rotationally fixed. Finally, the first clutch, the second clutch, the first brake, the second brake, the third brake, and the fourth brake are engaged in combinations of at least two in order to rotationally fix the output shaft. 
     In one example, engaging the first clutch, the second clutch, the first brake, the second brake, the third brake, and the fourth brake in combinations of at least two includes engaging the third brake and the fourth brake to rotationally fix the output shaft. 
     In another example, engaging the first clutch, the second clutch, the first brake, the second brake, the third brake, and the fourth brake in combinations of at least two includes engaging the first clutch, the second brake, and the third brake to rotationally fix the output shaft. 
     In yet another example, engaging the first clutch, the second clutch, the first brake, the second brake, the third brake, and the fourth brake in combinations of at least two includes engaging the first clutch, the first brake, and third brake to rotationally fix the output shaft. 
     In yet another example, determining that the output shaft of the transmission should be rotationally fixed includes sensing that the motor vehicle is at a negative speed and sensing that a throttle position or accelerator pedal position is below a predetermined value. 
     In another embodiment, a method for controlling a transmission in a motor vehicle includes providing a launch clutch, providing a transmission having an input member connected to the launch clutch, an output member, first, second, third, and fourth planetary gear sets each having a sun gear, a ring gear, and a carrier, wherein the ring gear of the first planetary gear set is connected with the ring gear of the second planetary gear set, the carrier of the first planetary gear set is connected with the carrier of the second planetary gear set and the sun gear of the third planetary gear set, the ring gear of the third planetary gear set is connected with the carrier of the fourth planetary gear set, and the carrier of the third planetary gear set is connected with the ring gear of the fourth planetary gear set, and wherein a first clutch connects the sun gear of the second planetary gear set with the carrier of the third planetary gear set and the ring gear of the fourth planetary gear set, a second clutch connects the sun gear of the second planetary gear set with the sun gear of the fourth planetary gear set, a first brake connects the sun gear of the first planetary gear set with a stationary member, a second brake connects the ring gears of the first and second planetary gear sets with the stationary member, a third brake connects the sun gear of the third planetary gear set and the carriers of the first and second planetary gear sets with the stationary member, and a fourth brake connects the carrier of the third planetary gear set and the ring gear of the fourth planetary gear set with the stationary member, commanding the transmission into a Drive mode of operation, determining that the output shaft of the transmission should be rotationally fixed, and engaging the first clutch, the second clutch, the first brake, the second brake, the third brake, and the fourth brake in combinations of at least two in order to rotationally fix the output shaft. 
     Further features, aspects and advantages of the present invention will become apparent by reference to the following description and appended drawings wherein like reference numbers refer to the same component, element or feature. 
    
    
     
       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 an embodiment of a nine speed transmission according to the present invention; 
         FIG. 2  is a diagrammatic view of an embodiment of a nine speed transmission according to the present invention; and 
         FIG. 3  is a truth table presenting the state of engagement of the various torque transmitting elements in each of the available forward and reverse speeds or gear ratios of the transmission illustrated in  FIGS. 1 and 2 . 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
     Referring now to  FIG. 1 , an embodiment of a nine speed transmission  10  is illustrated in a lever diagram format. A lever diagram is a schematic representation of the components of a mechanical device such as an automatic transmission. Each individual lever represents a planetary gear set wherein the three basic mechanical components of the planetary gear set are each represented by a node. Therefore, a single lever contains three nodes: one for the sun gear, one for the planet gear carrier, and one for the ring gear. The relative length between the nodes of each lever can be used to represent the ring-to-sun ratio of each respective gear set. These lever ratios, in turn, are used to vary the gear ratios of the transmission in order to achieve appropriate ratios and ratio progression. Mechanical couplings or interconnections between the nodes of the various planetary gear sets are illustrated by thin, horizontal lines and torque transmitting devices such as clutches and brakes are presented as interleaved fingers. If the device is a brake, one set of the fingers is grounded. Further explanation of the format, purpose and use of lever diagrams can be found in SAE Paper 810102, “The Lever Analogy: A New Tool in Transmission Analysis” by Benford and Leising which is hereby fully incorporated by reference. 
     The transmission  10  includes an input shaft or member  12 , a first planetary gear set  14  having three nodes: a first node  14 A, a second node  14 B and a third node  14 C, a second planetary gear set  16  having three nodes: a first node  16 A, a second node  16 B and a third node  16 C, a third planetary gear set  18  having three nodes: a first node  18 A, a second node  18 B and a third node  18 C, a fourth planetary gear set  20  having three nodes: a first node  20 A, a second node  20 B and a third node  20 C and an output shaft or member  22 . 
     The input member  12  is coupled to the first node  16 A of the second planetary gear set  16 . The output member  22  is coupled to the second node  18 B of the third planetary gear set  18  and the second node  20 B of the fourth planetary gear set  20 . The second node  14 B of the first planetary gear set  14  is coupled to the second node  16 B of the second planetary gear set  16 . The third node  14 C of the first planetary gear set  14  is coupled to the third node  16 C of the second planetary gear set  16  and the first node  18 A of the third planetary gear set  18 . The second node  18 B of the third planetary gear set  18  is coupled to the second node  20 B of the fourth planetary gear set  20 . The third node  18 C of the third planetary gear set  18  is coupled to the third node  20 C of the fourth planetary gear set  20 . 
     A first clutch  26  selectively connects the first node  16 A of the second planetary gear set  16  and the input member  12  with the third node  18 C of the third planetary gear set  18  and the third node  20 C of the fourth planetary gear set  20 . A second clutch  28  selectively connects the first node  16 A of the second planetary gear set  16  and the input member  12  with the first node  20 A of the fourth planetary gear set  20 . A first brake  30  selectively connects the first node  14 A of the first planetary gear set  14  to a stationary member or a transmission housing  40 . A second brake  32  selectively connects the second node  14 B of the first planetary gear set  14  and the second node  16 B of the second planetary gear set  16  to a stationary member or transmission housing  40 . A third brake  34  selectively connects the third node  14 C of the first planetary gear set, the third node  16 C of the second planetary gear set  16 , and the first node  18 A of the third planetary gear set  18  to the stationary member or transmission housing  40 . A fourth brake  36  selectively connects the third node  18 C of the third planetary gear set  18  and the third node  20 C of the fourth planetary gear set  20  to the stationary member or transmission housing  40 . 
     Referring now to  FIG. 2 , a stick diagram presents a schematic layout of the embodiment of the nine speed transmission  10  according to the present invention. In  FIG. 2 , the numbering from the lever diagram of  FIG. 1  is carried over. The clutches, brakes, and couplings are correspondingly presented whereas the nodes of the planetary gear sets now appear as components of planetary gear sets such as sun gears, ring gears, planet gears and planet gear carriers. 
     For example, the first planetary gear set  14  includes a sun gear member  14 A, a planet gear carrier member  14 C and a ring gear member  14 B. The sun gear member  14 A is connected for common rotation with a first shaft or interconnecting member  42 . The ring gear member  14 B is connected for common rotation with a second shaft or interconnecting member  44 . The planet gear carrier member  14 C rotatably supports a set of planet gears  14 D (only one of which is shown) and is connected for common rotation with a third shaft or interconnecting member  46  and a fourth shaft or interconnecting member  48 . The planet gears  14 D are each configured to intermesh with both the sun gear member  14 A and the ring gear member  14 B. 
     The second planetary gear set  16  includes a sun gear member  16 A, a planet carrier member  16 C that rotatably supports a set of planet gears  16 D and  16 E, and a ring gear member  16 B. The sun gear member  16 A is connected for common rotation with the input member  12 . The ring gear member  16 B is connected for common rotation with the second shaft or interconnecting member  44 . The planet carrier member  16 C is connected for common rotation with the fourth shaft or interconnecting member  48  and a fifth shaft or interconnecting member  50 . The planet gears  16 D are each configured to intermesh with both the ring gear member  16 B and the planet gears  16 E. The planet gears  16 E are each configured to intermesh with both the planet gears  16 D and the sun gear  16 A. 
     The third planetary gear set  18  includes a sun gear member  18 A, a ring gear member  18 B and a planet carrier member  18 C that rotatably supports a set of planet gears  18 D. The sun gear member  18 A is connected for common rotation with the fifth interconnecting member  50 . The ring gear member  18 B is connected for common rotation with a sixth shaft or interconnecting member  52 . The planet carrier member  18 C is connected for common rotation with a seventh shaft or interconnecting member  54  and with an eighth shaft or interconnecting member  56 . The planet gears  18 D are each configured to intermesh with both the sun gear member  18 A and the ring gear member  18 B. 
     The fourth planetary gear set  20  includes a sun gear member  20 A, a ring gear member  20 C and a planet carrier member  20 B that rotatably supports a set of planet gears  20 D. The sun gear member  20 A is connected for common rotation with a ninth shaft or interconnecting member  58 . The ring gear member  20 C is connected for common rotation with the seventh interconnecting member  54 . The planet carrier member  20 B is connected for common rotation with the sixth interconnecting member  52  and with the output member  22 . The planet gears  20 D are each configured to intermesh with both the sun gear member  20 A and the ring gear member  20 C. 
     The input shaft or member  12  is continuously connected to a dry clutch launch device  60 . The dry clutch launch device  60  is selectively connected to an engine or other prime mover (not shown). The output shaft or member  22  is preferably continuously connected with the final drive unit or transfer case (not shown). 
     The torque-transmitting mechanisms or clutches  26 ,  28  and brakes  30 ,  32 ,  34 ,  36  allow for selective interconnection of the shafts or interconnecting members, members of the planetary gear sets and the housing. For example, the first clutch  26  is selectively engageable to connect the eighth interconnecting member  56  with the input member  12 . The second clutch  28  is selectively engageable to connect the ninth interconnecting member  58  with the input member  12 . The first brake  30  is selectively engageable to connect the first interconnecting member  42  to the stationary member or transmission housing  40  in order to restrict the sun gear member  14 A of the first planetary gear set  14  from rotating relative to the stationary member or transmission housing  40 . The second brake  32  is selectively engageable to connect the second interconnecting member  44  to the stationary member or transmission housing  40  in order to restrict the ring gear member  14 B of the first planetary gear set  14  and the ring gear member  16 B of the second planetary gear set  16  from rotating relative to the stationary member or transmission housing  40 . The third brake  34  is selectively engageable to connect the third interconnecting member  46  to the stationary member or transmission housing  40  in order to restrict the planet carrier member  14 C of the first planetary gear set  14 , the planet carrier member  16 C of the second planetary gear set  16 , and the sun gear  18 A of the third planetary gear set  18  from rotating relative to the stationary member or transmission housing  40 . The fourth brake  36  is selectively engageable to connect the seventh interconnecting member  54  to the stationary member or transmission housing  40  in order to restrict the planet carrier member  18 C of the third planetary gear set  18  and the ring gear member  20 C of the fourth planetary gear set  20  from rotating relative to the stationary element or transmission housing  40 . 
     Referring now to  FIGS. 2 and 3 , the operation of the embodiment of the nine speed transmission  10  will be described. It will be appreciated that the transmission  10  is capable of transmitting torque from the input shaft or member  12  to the output shaft or member  22  in at least nine forward speed or torque ratios and at least one reverse speed or torque ratio. Each forward and reverse speed or torque ratio is attained by engagement of one or more of the torque-transmitting mechanisms (i.e. first clutch  26 , second clutch  28 , first brake  30 , second brake  32 , third brake  34 , and fourth brake  36 ), as will be explained below.  FIG. 3  is a truth table presenting the various combinations of torque transmitting mechanisms that are activated or engaged to achieve the various gear states. Actual numerical gear ratios of the various gear states are also presented although it should be appreciated that these numerical values are exemplary only and that they may be adjusted over significant ranges to accommodate various applications and operational criteria of the transmission  10 . An example of the gear ratios that may be obtained using the embodiments of the present invention are also shown in  FIG. 3 . Of course, other gear ratios are achievable depending on the gear diameter, gear teeth count and gear configuration selected. 
     To establish reverse gear, the first brake  30  and the fourth brake  36  are engaged or activated. The first brake  30  connects the first interconnecting member  42  to the stationary member or transmission housing  40  in order to restrict the sun gear member  14 A of the first planetary gear set  14  from rotating relative to the stationary member or transmission housing  40 . The fourth brake  36  connects the seventh interconnecting member  54  to the stationary member or transmission housing  40  in order to restrict the planet carrier member  18 C of the third planetary gear set  18  and the ring gear member  20 C of the fourth planetary gear set  20  from rotating relative to the stationary element or transmission housing  40 . Likewise, the nine forward ratios are achieved through different combinations of clutch and brake engagement, as shown in  FIG. 3 . 
     During certain operating conditions, it is desirable to hold the transmission output shaft stationary while in a Drive mode of operation, such as holding the motor vehicle on a hill. The determination whether to fix the output shaft while in Drive includes sensing a negative speed using a bi-directional sensor. If the motor vehicle is in Drive with a negative speed and below a pre-determined throttle or accelerator pedal position (for example, less than 5% engagement) then holding the output shaft stationary would be desired. The output shaft would be released when throttle or accelerator pedal positions was sensed to be above the pre-determined value. In order to not engage the dry launch clutch  60 , a combination of the clutches  26 ,  28  and brakes  30 ,  32 ,  34 , and  36  must be engaged to hold the transmission output shaft stationary. With reference to  FIG. 1 , in order to lock the output shaft  22  for any transmission corresponding to the lever diagram, there are three alternative engagement/disengagement strategies: (1) nodes  18 C/ 20 C and  18 A are grounded (or connected to a stationary housing); (2) the input shaft  12  is disconnected by disengaging the dry launch clutch  60  and nodes  14 B/ 16 B,  18 C/ 20 C, and  18 A are grounded (or connected to a stationary housing); or (3) the input shaft  12  is disconnected by disengaging the dry launch clutch  60  and nodes  14 A,  14 B/ 16 B, and  18 C/ 20 C are grounded (or connected to a stationary housing). With reference to  FIG. 2 , in order to lock the output shaft  22 , there are three alternative engagement/disengagement strategies: (1) apply or engage the brakes  34  and  36 ; (2) apply or engage the clutch  26  and the brakes  32  and  34 ; or (3) apply or engage the clutch  26  and the brakes  30  and  34 . 
     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.