Abstract:
A method of controlling a torque-transmitting mechanism in a multi-speed transmission includes providing structure forming a pressurizable reaction chamber at a reaction surface of an apply piston opposing an apply surface of the piston. The reaction chamber is pressurized to a first pressure during engagement of the torque-transmitting mechanism to establish a first speed ratio and a first torque capacity. The reaction chamber is pressurized to a second pressure level during engagement of the torque-transmitting mechanism to establish a second speed ratio and a second torque capacity. Thus, because pressure in the reaction chamber may be controllably varied, a greater reaction pressure is established during the second speed ratio, allowing a greater apply pressure level to be used to establish the second torque capacity. A clutch capacity control system is also provided that allows better control of torque-transmitting mechanisms engagable in different speed ratios to establish different torque capacities.

Description:
TECHNICAL FIELD  
       [0001]     The invention relates to torque-transmitting mechanisms in multi-speed transmissions. Specifically, the invention relates to control of torque capacity in torque-transmitting mechanisms.  
       BACKGROUND OF THE INVENTION  
       [0002]     Modern multi-speed transmissions utilize torque-transmitting mechanisms such as rotating type clutches and stationary clutches to transfer torque at various speed ratios through the transmission. Frequently, a torque-transmitting mechanism may be engaged in more than one fixed speed ratio (sometimes referred to as a gear ratio), i.e., the torque-transmitting mechanism is reused in the engagement schedule of the transmission. In these cases, a different torque capacity (also referred to as clutch capacity) is often required for the torque-transmitting mechanism in one gear ratio than in the other. For example, in a lower gear ratio, higher torque capacity is generally required at the engaged clutch than in a higher gear ratio. Torque-transmitting mechanisms must be designed to handle the maximum required torque capacity. This quality is referred to as the torque capacity of the clutch. When the ratio of the torque capacity for the torque-transmitting mechanism in the gear ratio requiring the maximum capacity divided by the torque capacity needed in the gear ratio required the minimum torque capacity exceeds about 3.0, it becomes challenging to control the apply and release of the torque-transmitting mechanism in the gear ratio with the lower torque capacity. Because the apply pressure will be about one-third or less of the apply pressure in the gear ratio requiring the maximum apply pressure, factors such as the tolerance on a return spring for the apply piston (i.e., the minimum force necessary to compress the return spring) affect the control of the torque-transmitting mechanism. For instance, the tolerance on the return spring may become a significant percentage of the total force on the apply piston necessary to move and engage the torque-transmitting mechanism in the gear ratio with the lower torque capacity. Additionally, the apply pressure on the piston may be so low in the gear ratio with the lower torque capacity that rotating shaft seals on the piston may not be sufficiently seated, producing a variable leak and thus compromising control of the torque-transmitting mechanism. Drag of the piston seal may also become a high percentage of the total force required to move the apply piston in the lower torque capacity instance. Change in the force of the return spring with stroke of the apply piston may also become a significant percentage of the total force on the torque-transmitting mechanism in the gear ratio requiring lower torque capacity. Finally, a solenoid valve regulating the pressure to engage the torque-transmitting mechanism is typically regulated at a very low pressure in the gear ratio requiring minimum torque capacity, and, therefore, the solenoid tolerance and hysteresis become a high percentage of the total pressure. This may make effective calibration of the apply pressure and, thus, the engagement of the torque-transmitting mechanism difficult.  
         [0003]     One solution for achieving the different torque capacities required in different gear ratios at the same torque-transmitting mechanism is to use two different apply pistons having different areas with separate feed oils. Both of the pistons are used in the speed ratio requiring a higher torque capacity at the torque-transmitting mechanism and only one of the pistons is used in the speed ratio with lower torque capacity at the torque-transmitting mechanism. However, in a multi-speed transmission in which more than one torque-transmitting mechanism is likely to require such a dual area piston, an inordinate number of feed holes required in the transmission main shaft to feed the various apply pistons could necessitate an undesirable increase in shaft diameter. Also a rotating shaft seal is required for each apply piston, which may decrease transmission efficiency due to drag.  
       SUMMARY OF THE INVENTION  
       [0004]     A method of controlling a torque-transmitting mechanism is provided that solves the problems associated with torque-transmitting mechanisms requiring different torque capacities in different speed ratios. The torque-transmitting mechanism is engagable by an apply piston having an apply surface and opposing reaction surface. The method includes providing structure forming a pressurizable reaction chamber at the reaction surface. The reaction chamber is pressurized to a first pressure during engagement of the torque-transmitting mechanism in a first speed ratio. The torque-transmitting mechanism has a first torque capacity when the reaction chamber is pressurized to the first pressure. The reaction chamber is pressurized to a second pressure greater than the first pressure during the engagement of the torque-transmitting mechanism in a second speed ratio. (As used in the claims, the “first speed ratio” and the “second speed ratio” are any two different speed ratios and are not either necessarily consecutive or the first and second forward speed ratios.) The torque-transmitting mechanism has a second torque capacity when the reaction chamber is pressurized to the second pressure. Because of the greater second pressure in the reaction chamber, a greater apply pressure may be applied to the apply surface to establish the second torque capacity than if a lower pressure (such as the first pressure) existed in the reaction chamber. Accordingly, with the greater apply pressure, engagement of the torque-transmitting mechanism in speed ratios requiring lower torque capacities is accomplished with greater control.  
         [0005]     Thus, because pressure in the reaction chamber may be varied, different apply pressures may be used to achieve a desired torque capacity. Applying the piston to establish the first of the two speed ratios may include establishing a first apply pressure at the apply surface and applying a piston to establish the second of the two speed ratios may include establishing a second apply pressure at the apply surface. Although the first torque capacity may be greater than the second torque capacity, the second reaction pressure may be greater than the first reaction pressure, thus allowing a larger apply pressure to be used to establish the lower second torque capacity; that is, an apply pressure that is at a level easier to control.  
         [0006]     The method may include providing structure forming the reaction chamber. A dam member, likely having an annular ring shape, positioned at the apply surface to create the reaction chamber therebetween may be used. The reaction chamber may also be sealed so that it is substantially leak free.  
         [0007]     The reaction pressure may be controlled in stages depending upon the speed ratio. For instance, the method may include directing oil through a valve to thereby increase pressure of the oil from the first apply pressure to the second reaction pressure. For instance, the apply pressure may be directed through a pressure regulator valve to decrease pressure of the oil from the first apply pressure to the second reaction pressure, thereby allowing a greater apply pressure to work against the second reaction pressure in moving the apply piston in the speed ratio requiring the lower torque capacity. An additional valve may be employed in conjunction with the pressure regulator valve. This valve may be switched between a first position in which oil of the first reaction pressure is provided to the reaction chamber and a second position in which oil at the second reaction pressure is provided to the reaction chamber. Alternatively, the additional valve may be a solenoid valve which is calibrated to move in multiple increments, i.e., from a first position to a second position to a third position to thereby control the reaction pressure at a first reaction pressure, a second reaction pressure, a third reaction pressure, etc.  
         [0008]     A method of controlling a torque-transmitting mechanism in a multi-speed transmission may also be described as establishing a first reaction pressure at the reaction surface during engagement of the torque-transmitting mechanism to establish the first of two speed ratios in which the torque-transmitting mechanism is engaged. The method may also include establishing a second reaction pressure at the reaction surface during engagement of the torque-transmitting mechanism to establish a second of the two speed ratios. The torque-transmitting mechanism has a first torque capacity in the first of the two speed ratios and a second torque capacity in the second of the two speed ratios. The apply piston is applied to establish the first speed ratio when the first reaction pressure is established and the second speed ratio when the second reaction pressure is established.  
         [0009]     A clutch capacity control system that solves the problem of controlling a clutch engaged at different torque capacities in different speed ratios of the transmission includes a plurality of clutch plates engagable to transfer torque. An apply piston moveable via fluid pressure to engage the clutch plates is also included. A dam member at least partially establishes a fluid filled reaction chamber opposing movement of the apply piston. A valve is controllable to vary fluid pressure within the reaction chamber, thereby requiring a corresponding variance in pressure applied to the apply piston to establish a predetermined torque capacity at the clutch plates. Preferably, the apply piston has an apply surface and an opposing reaction surface and the reaction chamber is located at the reaction surface. Because the clutch capacity control system allows control of fluid pressure in the reaction chamber, a return spring such as is typically employed to return the applied piston upon disengagement of the clutch is not required and is not used in the control system. The control system may be used with equal success on rotating-type apply pistons and stationary-type apply pistons.  
         [0010]     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 modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a schematic cross-sectional fragmentary view of a multi-speed transmission employing the clutch capacity control system of the present invention; and  
         [0012]      FIG. 2  is a schematic cross-sectional fragmentary view of the transmission of  FIG. 1  illustrating clutch capacity control systems employed in relation to several different torque-transmitting mechanisms. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]     The planetary transmission  14  includes an input shaft  17  continuously connected with an engine and torque converter (not shown), a planetary gear arrangement  18 , and an output shaft  19  continuously connected with a final drive mechanism (not shown). The planetary gear arrangement  18  includes three planetary gear sets  20 ,  30  and  40 , viewed from left to right in  FIG. 1 .  
         [0014]     Referring to  FIG. 2 , the 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 .  
         [0015]     Referring again to  FIG. 1 , the 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 gear member  34 .  
         [0016]     The 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 the pinion gears  37  which are long pinion gears interconnecting the planet carrier assembly member  36  with the planet carrier assembly member  46 . The planet carrier assembly member  46  also includes a plurality of pinion gears  48  rotatably mounted on carrier member  39  to form a compound planetary gear set. 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 pinion gears  47 ,  48  also mesh with each other. The ring gear member  44  may be formed integrally with the ring gear member  34  such that a single elongated ring gear member forms both components. Alternatively, the ring gear member  34  and ring gear member  44  may be formed separately and connected together (as shown in  FIGS. 1 and 2 ). The planetary gear set  40  is a compound planetary gear set.  
         [0017]     The planetary gear arrangement  18  also includes six torque-transmitting mechanisms  50 ,  52 ,  54 ,  56 ,  58 ,  59 . The torque-transmitting mechanisms  50 ,  52 ,  58  are stationary-type torque-transmitting mechanisms, commonly termed brakes or reaction clutches. The torque-transmitting mechanisms  54 ,  56 ,  59  are rotating-type torque-transmitting mechanisms, commonly termed clutches. Each torque-transmitting mechanism  50 ,  52 ,  54 ,  56 ,  58  and  59  has two sets of axially spaced plates  70 ,  72  which may be placed in frictional contact with one another via an apply piston, as discussed below, to engage the torque-transmitting mechanism. Only the plates of the torque-transmitting mechanism  50  are labeled in  FIG. 2 ; however, those skilled in the arts will readily recognize two sets of plates and their functions for each of the torque-transmitting mechanisms of  FIGS. 1 and 2 .  
         [0018]     The input shaft  17  is continuously connected with the ring gear member  24  (see  FIG. 2 ), and the output shaft  19  is continuously connected with the ring gear member  44  (see  FIG. 1 ). The carrier member  39  is selectively connectable with the transmission housing  60  through the brake  50 . The sun gear member  32  is selectively connectable with the transmission housing  60  through the brake  52 . The carrier member  29  is selectively connectable with the sun gear member  32  through the clutch  54 . The ring gear member  24  is selectively connectable with the carrier member  49  through the clutch  56 . The sun gear member  22  is selectively connectable with the transmission housing  60  through the clutch  58 . The carrier member  29  is selectively connectable with the sun gear member  42  through the clutch  59 .  
         [0019]     The torque-transmitting mechanisms  50 ,  52 ,  54 ,  56 ,  58 ,  59  are selectively engaged in combinations of three to provide seven forward speed ratios and one reverse speed ratio. The numerical values of these ratios, discussed below, assume the following ring gear/sun gear tooth ratio: 1.47 for the planetary gear set  20 , 2.00 for the planetary gear set  30  and 1.47 for the planetary gear set  40 . It should also be noted that the torque-transmitting mechanisms  50 ,  58  remain engaged through the neutral condition, thereby simplifying the forward/reverse interchange.  
         [0020]     To establish the reverse speed ratio, the torque-transmitting mechanisms  50 ,  54  and  58  are engaged. The overall numerical value of the reverse speed ratio is −3.361.  
         [0021]     The first forward speed ratio is established with the engagement of the torque-transmitting mechanisms  50 ,  58 ,  59 . The overall numerical value of the first forward speed ratio is 4.419.  
         [0022]     The second forward speed ratio is established with the engagement of the torque-transmitting mechanisms  52 ,  58 ,  59 . The overall numerical value of the second forward speed ratio is 2.593.  
         [0023]     The third forward speed ratio is established with the engagement of the torque-transmitting mechanisms  54 ,  58 ,  59 . The overall numerical value of the third forward speed ratio is 1.680.  
         [0024]     The fourth forward speed ratio is established with the engagement of the torque-transmitting mechanisms  56 ,  58 ,  59 . The overall numerical value of the fourth forward speed ratio is 1.182.  
         [0025]     The fifth forward speed ratio is established with the engagement of the torque-transmitting mechanisms  54 ,  56 ,  59 . The numerical value of the fifth forward speed ratio is 1.  
         [0026]     The sixth forward speed ratio is established with the engagement of the torque-transmitting mechanisms  54 ,  56 ,  58 . The numerical value of the sixth forward speed ratio is 0.832.  
         [0027]     The seventh forward speed ratio is established with the engagement of the torque-transmitting mechanisms  52 ,  56 ,  58 . The numerical value of the seventh forward speed ratio is 0.667.  
         [0028]     As shown, the torque-transmitting mechanism  50  is applied by the piston  70 A by application of pressurized fluid in the apply chamber  72 A. Oil is fed to the apply chamber  72 A to create an apply pressure acting on an apply surface or area  73 A of the piston  70 A. A reaction chamber  74 A is formed between the piston  70 A and a dam member  76 A. The dam member  76 A sealingly interfaces with the piston  70 A in a manner that seals the reaction chamber  74 A such that it is essentially leak free and is able to maintain a controlled reaction pressure acting on a reaction area or surface  75 A of the piston  70 A. Thus, the reaction pressure counteracts some of the apply pressure. The greater the apply pressure for a given reaction pressure, the greater force is applied to engaged the plates  70 ,  72  resulting in a greater torque capacity (i.e., ability to transfer torque between planetary gear members (for a rotating-type clutch) or between a planet gear member and the transmission housing (for a brake)). Any increase in reaction pressure necessitates a corresponding increase in apply pressure in order to achieve a given torque capacity at the engaged plates  70 ,  72  of the torque-transmitting mechanism  50 .  
         [0029]     Because the pressure in the reaction chamber  74 A may be controlled, no return spring is necessary to return the apply piston  70 A to a nonapply/nonengaged position upon clutch release (i.e., upon controlled decrease in apply pressure causing disengagement of the plates  70 ,  72 ). None of the torque-transmitting mechanisms illustrated in  FIGS. 1 and 2  and discussed herein require a piston return spring.  
         [0030]     The torque-transmitting mechanism  52  is applied by the piston  70 B a by application of pressurized fluid in the apply chamber  72 B. A reaction chamber  74 B similar in function to reaction chamber  74 A is formed between the apply piston  70 B and a dam member  76 B similar in function to dam member  76 A. Fluid having an apply pressure acts on an apply surface  73 B of piston  70 B and fluid in the reaction chamber  74 B having a reaction pressure acts on a reaction surface  75 B.  
         [0031]     The torque-transmitting mechanism  54  is applied by the piston  70 C as a result of application of pressurized fluid in the apply chamber  72 C. The application arm  71  of the piston  70 C is castellated to pass through the plates of the clutch  59  for applying the clutch  54 . The reaction chamber  74 C is formed between the apply piston  70 C and a dam member  76 C. The reaction chamber  74 C is provided with pressure controlled fluid having a reaction pressure in order to counterbalance some of the applied force resulting from the apply pressure and thereby allowing a greater apply pressure to be utilized to obtain a desired torque capacity at the torque-transmitting mechanism  54 . Fluid having an apply pressure acts on an apply surface  73 C of the piston  70 C and fluid in the reaction chamber  74 C having a controlled reaction pressure acts on the reaction surface  75 C. The reaction chamber  74 C may also serve as a balance dam chamber to counterbalance centrifugal forces of fluid in the chamber  72 B.  
         [0032]     The torque-transmitting mechanism  56  is applied by the piston  70 D when pressurized fluid is provided in the apply chamber  72 D. A reaction chamber  74 D similar in function to reaction chamber  74 A is formed between the apply piston  70 D and a dam member  76 D similar in function to dam member  76 A. Fluid having an apply pressure acts on an apply surface  73 D of the piston  70 D and fluid in the reaction chamber  74 D having a controlled reaction pressure acts on the reaction surface  75 D. The reaction chamber  74 D also serves as a balance dam chamber to counterbalance centrifugal forces of the fluid in the apply chamber  72 D.  
         [0033]     The torque-transmitting mechanism  58  is applied by the piston  70 E when pressurized fluid is provided in the apply chamber  72 E. A reaction chamber  74 E similar in function to reaction chamber  74 A is formed between the apply piston  70 E and a dam member  76 E similar in function to dam member  76 A. Fluid having an apply pressure acts on one side of the piston (on its apply surface  73 E) and fluid having a controlled reaction pressure acts on the opposing side of piston (on its reaction surface  75 E).  
         [0034]     The torque-transmitting mechanism  59  is applied by the piston  70 F when pressurized fluid is provided in the apply chamber  72 F. A reaction chamber  74 F similar in function to reaction chamber  74 A is formed between the apply piston  70 F and a dam member  76 F similar in function to dam member  76 A. Fluid having an apply pressure acts on one side of the piston (on its apply surface  73 F) and fluid having a controlled reaction pressure acts on the opposing side of piston (on its reaction surface  75 F). The reaction chamber  74 F also serves as a balance dam chamber to counterbalance centrifugal forces of the fluid in the apply chamber  72 F.  
         [0035]      FIG. 1  also shows an optional freewheeler  100 , including a race  102 , a roller  104 , and a cam  106 . The freewheeler  100  is operative to selectively connect the carrier member  39  with the transmission housing  60 .  
         [0036]     Referring again to  FIG. 2 , The sun gear member  22  is supported on a rotatable hollow sun gear shaft  110 , which has substantially radially-extending apertures  112 ,  114 ,  116 ,  118  which are positioned to provide fluid to the apply chamber  72 C, reaction chamber  74 E, apply chamber  72 F, and reaction chamber  74 F, respectively, as shown in  FIG. 2 . The apertures (also referred to as channels)  112 ,  114 ,  116  and  118  intersect the hollowed portion  117  of the sun gear shaft  110 . Seals are provided adjacent the channels  112 ,  114 ,  116 ,  118  to prevent leakage therethrough. Seals and bearing  137  are operative to prevent leakage of the fluid which is fed into the channels  112 ,  114 ,  116 ,  118 . The bearing  129  is also used as a seal. The chamber  126  feeds oil through the channels  128  into the channel  116 . A plurality of similar circumferentially-spaced chambers are also utilized, with separate ones of these chambers feeding respective ones of channels  112 ,  114  and  118  via other channels  151 ,  153  and  130 , shown in phantom, in the component  115 ). Channels  128 ,  130 ,  151  and  153  are radially and axially spaced from one another, each fluidly connected with a separate one of the circumferentially-spaced chambers such as chamber  126 . From the channel  116 , fluid enters the apply chamber  72 F through the channel  132 . From the channel  118 , fluid enters the reaction chamber  74 F through the channel  134 . From the channel  114 , fluid enters the apply chamber  72 C through the channel  136 . From the channel  112 , fluid enters the reaction chamber  74 C through the channel  138 .  
         [0037]     The chamber  126  (and the other circumferentially-spaced chambers) also feed the apply chamber  72 D and reaction chamber  74 D of the clutch  56  through channels  140 ,  142  in the input shaft  17 . The channels  140 ,  142  are sealed by seals.  
         [0038]     In this manner, fluid for applying the torque-transmitting mechanisms  54 ,  59  is fed through the sun gear shaft  110 , which is splined to the sun gear  22  at the splines  150 . The other torque-transmitting mechanism  50 ,  52  and  58  are also supplied with fluid to their respective apply chambers and reaction chambers in a controlled and leak free manner. With respect to the stationary-type torque-transmitting mechanisms  50 ,  52 ,  58 , fluid is fed to the respective apply chambers and reaction chambers as follows. The apply chamber  72 A for torque-transmitting mechanism  50  receives fluid from a transmission valve body (not shown) through a channel fluidly connected thereto but not visible in the cross-sectional view of  FIG. 2 . The reaction chamber receives fluid from the valve body through chamber  83  and, from there, through fluidly connected channels  84 ,  86 , and  88 . The apply chamber  72 B for torque-transmitting mechanism  52  receives fluid from the valve body through a chamber similar to chamber  83  and circumferentially-spaced therefrom, which feeds oil to a radial channel circumferentially-spaced from channel  84  and at the same axial location as channel  84  and then through axial channel  85 . Finally, fluid is supplied to apply chamber  72 E for torque-transmitting mechanism  58  from the valve body and through radial channel  86 . Fluid is supplied to the reaction chamber  74 E for torque-transmitting mechanism  58  from the valve body through radially channel  88 .  
         [0039]     Fluid supplied from the valve body is supplied at individually controlled pressures to each of the respective apply and reaction chambers. Referring to  FIG. 3 , the fluid supplied to each of the torque-transmitting mechanisms is under the control of a control unit  160  which may be an electronic control unit for an entire vehicle or a separate control unit for the transmission. Because the reaction chambers must have a reaction pressure that may be varied separately from the apply pressure in each of the respective torque-transmitting mechanisms, fluid entering the various chambers must be controlled by the control unit  160  to obtain various pressures at the respective chambers. Thus, referring to  FIG. 3 , the control unit  160  is operatively connected to a switching valve  162 . Fluid at a line pressure (e.g., 60 to 240 pounds per square inch) is routed through pressure regulator valve  164  to cause a pressure drop from the line pressure in channel  90  to one-half of line pressure in channel  92 . A second pressure regulator valve  166  controls pressure routed at line pressure through channel  94  to a compensation oil pressure of about  13  pounds per square inch in channel  96 . If it is desired to supply a reaction pressure that is a fraction of the apply pressure, such as one-half of the apply pressure, the switching valve  162  is controlled by the control unit  160  to move between a first position  95  (in which it blocks flow from channel  92  and allows flow at compensation oil pressure from channel  96 ) to a second position  97  (in which blocks channel  96  and permits flow at one-half of line pressure from channel  92  to channel  98 . The fluid directed through the switching valve  162  is then routed from channel  98  to a respective reaction chamber of one or more of the torque-transmitting mechanisms.  
         [0040]     In one embodiment, switching valve  162  is controlled to permit flow from channel  96  in lower speed ratios, where greater torque capacity may be required at a specific torque-transmitting mechanism (i.e., the first through fourth forward speed ratios described above) so that fluid may be supplied to one or more of the reaction chambers through channel  96  at a controlled compensation oil pressure. In higher speed ratios, where lower torque capacity may be required at a specific torque-transmitting mechanism, valve  164  is controlled to permit fluid to be supplied to a reaction chamber through channel  92  at one-half of line pressure. Thus, a greater apply pressure may be utilized in the higher speed ratios than if fluid at the compensation oil pressure were supplied to the reaction chamber, allowing greater control of the torque-transmitting mechanism, as described above.  
         [0041]     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.