Abstract:
A heavy-duty industrial transmission is provided that can be implemented in a frac pump system with planetary gearsets with straightforward shift methodologies, slow back-driven speeds, and no recirculating torque in any of the ranges. The heavy-duty transmission has a high number of ranges and may be configured with no reverse range, no countershaft, no overdrive range(s), small and consistent steps of ratios between ranges, and a deep or large reduction ratio of the lowest range, such as at least about a 5:1 reduction. The heavy-duty industrial transmission may have a four-stage planetary arrangement that is configured to provide nine (9) ranges for the transmission that only requires two double pack shifts, with the remaining shifts being single pack shifts.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims a benefit of priority under 35 USC §119(e) to U.S. Provisional Patent Application No. 62/280,219 filed Jan. 19, 2016, the entire contents of which are hereby expressly incorporated by reference into the present application. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Field of the Invention 
         [0003]    The preferred embodiments are directed to industrial transmissions and, more particularly, to a heavy-duty industrial transmission without reversing action or reverse gears and without countershafts. The present transmissions may be used in stationary applications like those within the well drilling and completion segments of the oil and gas industries, such as fracturing (frac) pump systems used for well stimulation by hydraulically fracturing subterranean formations. 
         [0004]    Discussion of the Related Art 
         [0005]    Hydraulically fracturing subterranean formations is a common way of increasing the porosity of and, thus, flow rate through production zones that feed boreholes of wells that remove underground resources like oil and gas. Increasing the flow rate through the production zones correspondingly increases the productivity of the wells. 
         [0006]    Extreme hydraulic pressures are required for fracturing subterranean formations, for example, 10,000 psi or more. To achieve these pressures, frac pump systems include heavy-duty pumps that are powered by high horsepower engines, with heavy-duty transmissions delivering torque from the engines to the respective pumps. 
         [0007]    Heavy-duty transmissions used in frac pump systems are typically already existing heavy-duty mechanical transmissions that are designed for other applications. Since these existing heavy-duty transmissions are rated to handle the high horsepower engines that drive the pumps of the frac pump systems, the existing heavy-duty transmissions are repurposed for frac pump system uses. 
         [0008]    Commonly, these repurposed heavy-duty transmissions are from off-road or other heavy duty vehicles. Heavy-duty vehicle transmissions tend to be large and heavy with countershafts and other features which add to the overall size of the transmission housings needed to accommodate these internal components. These heavy-duty vehicle transmissions typically have a large number of speeds or ranges, such as six or more ranges, and a large number of ranges can be beneficial in frac pump systems. That is because, although only a few ranges may be used for a particular fracing application, other ranges may be used in other fracing applications, depending on the various pump sizes and well pressures that are needed for those applications. However, the ratios of the heavy-duty vehicle transmissions ranges tend to be spaced at inconsistent steps, whereby the reduction or gear ratio values of adjacent pairs of ranges tend to be different, to provide desired vehicle movement performance requirements. But inconsistent steps between ranges can make some of the ranges or groups of sequential ranges ill-suited for delivering power to high-pressure pumps of frac pump systems. Inconsistent steps can make it difficult to finely adjust pump driving speed through range changes while maintaining optimal engine RPM. Inconsistent steps may also include at least one large change in reduction ratio that the engine may not be able to power while overcoming the head pressure of the well, making the gear change too large for the engine to handle. Typical heavy-duty vehicle transmissions also include ranges that provide reversing action or reverse gears for backward travel and overdrive ranges for high speed travel. However, high-pressure pumps of frac pump systems are typically neither driven in reverse nor driven at speeds that are faster than engine speed or transmission input speed because driving the pumps at high speeds can produce heavy vibration in the equipment. 
         [0009]    Other existing heavy-duty transmissions used in frac pump systems include heavy-duty industrial transmissions used in other stationary applications. Although some planetary-type transmissions have been implemented in frac pump systems, many industrial transmissions used in frac pump systems have countershaft configurations and a large number of gears like heavy-duty vehicle transmissions. Heavy-duty industrial transmissions for stationary applications typically have a large number of gears or ranges, though again with ratios of the ranges tending to be spaced at inconsistent steps. 
         [0010]    In order to provide the large number of ranges, heavy-duty transmissions typically incorporate planetary gearsets or compound planetary gearsets. The planetary gearsets are controlled to direct power through different components of the planetary gearsets to provide the desired output gear ratios for ranges. Control includes actuating clutches to restrict or allow rotation of the various planetary gearset components, such as sun gears, planet gears, planet carriers, or ring gears to establish different power paths and output rotational speeds of the planetary gearsets. 
         [0011]    Control of compound planetary gearsets or multiple planetary gearsets can require actuating multiple clutches during a single shift event, such as a multipack shift. Multipack shifts are typically synchronized and closely coordinated, and these synchronized multipack shifts can be complicated to control. 
         [0012]    Controlling compound or multiple planetary gearsets typically cause(s) rotation of components of the planetary gearsets that are loaded and thus in the power path, but, in at least some of the ranges, also causes rotation of some components of the planetary gearsets that are not loaded. 
         [0013]    The loaded components of planetary gearsets can experience recirculating torque in at least some ranges with higher values. Although a transmission output torque value will be a multiplication of the transmission input torque value as a function of the reduction ratio for a particular range, internal torque values can be much higher than the output torque value of the transmission. These higher internal torque values can be transmitted through at least some of the loaded planetary gearset components as recirculating torque that is higher than the output torque value(s), depending on, for example, particular gear ratios within the planetary gearsets. High recirculating torque values can affect the use-life of the components experiencing the recirculating torque and therefor require internal components that are designed to handle the high recirculating torque values. 
         [0014]    The unloaded but rotating components of planetary gearsets are freely spinning on unloaded bearings at back-driven speeds. Some back-driven speeds can be very high. High back-driven speeds can cause roller bearings to be lightly loaded, which may result in skidding of the rollers in the bearing raceways. Skidding of the roller bearings in this way can result in high speed failures. 
         [0015]    Another challenge with the present application is that mounting space is limited within frac pump systems, which are commonly mounted on trailers that are pulled by on-road semi tractors. In order to help repurposed heavy-duty transmissions fit in limited spaces within frac pump systems, the heavy-duty transmissions are often directly or closely coupled. 
         [0016]    Overall, a heavy-duty transmission suitable for use in a frac pump system that allows the frac pump system to be brought smoothly online regardless of engine speed and has a relatively small size with robust construction and straightforward operation is desired. 
       SUMMARY OF THE INVENTION 
       [0017]    The preferred embodiments overcome the above-noted drawbacks by providing a heavy-duty industrial transmission that can be implemented in a frac pump system with planetary gearsets with straightforward shift methodologies, slow back-driven speeds, and no recirculating torque in any of the ranges. 
         [0018]    In accordance with a first aspect of the invention, the heavy-duty transmission has a high number of ranges with small and consistent steps of ratios between ranges and a deep or large reduction ratio of the lowest range, such as at least about a 5:1 reduction. The transmission has no reverse range, no countershaft, no overdrive range(s), so the transmission itself can be smaller than it would be if it had to accommodate these additional components. This allows the heavy-duty transmission to be compact enough to allow use with a torque converter in a frac pump system application and a deep enough reduction ratio at its lowest range to allow for relatively slow pump speeds and output flow while bringing the frac pump system online to reduce disruption of the well formation. 
         [0019]    In accordance with another aspect of the invention, a heavy-duty transmission includes a transmission housing, an input shaft arranged at least partially in the transmission housing receiving power into the heavy-duty transmission, and an output shaft arranged at least partially in the transmission housing delivering power out of the heavy-duty transmission. A center shaft is arranged in the transmission housing between and longitudinally aligned with the input and output shafts. A four-stage planetary arrangement selectively delivers power from the input shaft to the center shaft and from the center shaft to the output shaft. 
         [0020]    In accordance with another aspect of the invention, a four-stage planetary arrangement includes a front planetary section with a pair of front planetary gearsets and a back planetary section with a pair of back planetary gearsets. The front planetary section may include a front set of three clutches for establishing three distinct power flow paths through different components of the pair of front planetary gearsets. The back planetary section may include a back set of three clutches for establishing three distinct powerful paths through different components of the pair of back planetary gearsets. The clutches engage various ones of sun gears, planet carriers, and ring gears at the front and back planetary sections to ground and therefore hold stationary corresponding components or lock various components into rotational unison with each other to provide the distinct power paths that correspond to achieve reductions or gear ratios of the ranges of the transmission. 
         [0021]    In accordance with another aspect of the invention, the four-stage planetary arrangement is controlled to provide a shift methodology in which range changes are achieved primarily by single pack shifts in the front planetary section, with relatively few double pack shifts in which shifts occur in both the front and back planetary sections. This may include controlling three clutches in the front planetary section to activate or engage only a single one of the three clutches of the front set at any given time to provide three power paths through the front planetary section for three clutch engagement states. Of the three power paths corresponding to the three clutch engagement states in the front planetary section, two may provide reductions through the front planetary gearset and the third may provide lockup or no reduction through the front planetary gearset. The three clutches in the back planetary section may be controlled to activate or engage only a single one of the three clutches of the back set at any given time to provide three power paths through the back planetary section for the three clutch engagement states. Each power path and clutch engagement state in the back planetary section may be held during consecutive power path and clutch engagement state changes in the front planetary section, so that clutch activation and deactivation in the back planetary section occurs less frequently than in the front planetary section. The three power paths corresponding to the three clutch engagement states in the back planetary section may provide two reductions through the back planetary gearset and the third may provide lockup or no reduction through the back planetary gearset. 
         [0022]    In accordance with another aspect of the invention, a four-stage planetary arrangement includes a shift methodology in which, starting at the lowest range, the back planetary section is held in a first state with a first back end power path with one of the clutches in the back planetary section remaining engaged during two consecutive shift events in the front planetary section. The two consecutive single pack shift events occur to shift from 1 st  range to 2 nd  range and from 2 nd  range to 3 rd  range, in which only a single clutch in the front planetary section is disengaged and another clutch is engaged. A double pack shift may provide a range change from 3 rd  range to 4 th  range. During the double pack shift, in the back planetary section, the previously engaged clutch is released and another clutch is engaged to shift the back planetary section to a second state with a second back end power path. During the double pack shift to provide the 4 th  range, the front planetary section returns to the first state with the first power path corresponding to that of the 1 st  range. Two more consecutive single pack shift events in the front planetary section are used to shift from 4 th  range to 5 th  range and from 5 th  range to 6 th  range while the back planetary gearset remains in the second state with the second back end power path. Another double pack shift may provide a range change from 6 th  range to 7 th  range. During the double pack shift, in back planetary section, the previously engaged clutch is released and another clutch is engaged to shift the back planetary section to a third state with a third back end power path. During the double pack shift to provide the 7 th  range, the front planetary section again returns to the first state with the first power path corresponding to that of the 1 st  range. Two more consecutive single pack shift events in the front planetary section are used to shift from 7 th  range to 8 th  range and from 8 th  range to 9 th  range while the back planetary gearset remains in the third state with third back end power path. 
         [0023]    In accordance with another aspect of the invention, in the front planetary section of the four-stage planetary arrangement, the planetary gearsets may be connected to each other through multiple connections. The ring gears of the planetary gearsets in the front planetary section may be connected to each other and the planet carriers of the planetary gearsets in the front planetary section may also be connected to each other. This may be done with a relatively wide common ring gear having two spaced-apart internally toothed surfaces that define the two ring gears for the pair of planetary gearsets in the front planetary section. A planet carrier assembly can be arranged at least partially radially outward of the ring gears to provide a connection between the planet carriers in the front planetary section. In the back planetary section, the front-most planet carrier may be connected to the back-most ring gear. 
         [0024]    These and other features and advantages of the invention will become apparent to those skilled in the art from the following detailed description and the accompanying drawings. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    Preferred exemplary embodiments of the invention are illustrated in the accompanying drawings in which like reference numerals represent like parts throughout, and in which: 
           [0026]      FIG. 1  is a schematic illustration of a heavy-duty transmission used in a frac pump system at a drilling site; 
           [0027]      FIG. 2  is a pictorial view from above and in front of a heavy-duty transmission of  FIG. 1 ; 
           [0028]      FIG. 3  is a pictorial view from above and behind the heavy-duty transmission of  FIG. 2 ; 
           [0029]      FIG. 4  is a cross-sectional view of the heavy-duty transmission of  FIG. 2 ; 
           [0030]      FIG. 5  is an enlarged cross-sectional view of a portion of the heavy-duty transmission of  FIG. 2 ; 
           [0031]      FIG. 6  is a simplified schematic view showing a 1 st  range power path of the heavy-duty transmission of  FIG. 2 ; 
           [0032]      FIG. 7  is a simplified schematic view showing a 2 nd  range power path of the heavy-duty transmission of  FIG. 2 ; 
           [0033]      FIG. 8  is a simplified schematic view showing a 3 rd  range power path of the heavy-duty transmission of  FIG. 2 ; 
           [0034]      FIG. 9  is a simplified schematic view showing a 4 th  range power path of the heavy-duty transmission of  FIG. 2 ; 
           [0035]      FIG. 10  is a simplified schematic view showing a 5 th  range power path of the heavy-duty transmission of  FIG. 2 ; 
           [0036]      FIG. 11  is a simplified schematic view showing a 6 th  range power path of the heavy-duty transmission of  FIG. 2 ; 
           [0037]      FIG. 12  is a simplified schematic view showing a 7 th  range power path of the heavy-duty transmission of  FIG. 2 ; 
           [0038]      FIG. 13  is a simplified schematic view showing an 8 th  range power path of the heavy-duty transmission of  FIG. 2 ; 
           [0039]      FIG. 14  is a simplified schematic view showing a 9 th  range power path of the heavy-duty transmission of  FIG. 2 ; 
           [0040]      FIG. 15  is a cross-sectional view showing a 1 st  range power path of the heavy-duty transmission of  FIG. 2 ; 
           [0041]      FIG. 16  is a cross-sectional view showing a 2 nd  range power path of the heavy-duty transmission of  FIG. 2 ; 
           [0042]      FIG. 17  is a cross-sectional view showing a 3 rd  range power path of the heavy-duty transmission of  FIG. 2 ; 
           [0043]      FIG. 18  is a cross-sectional view showing a 4 th  range power path of the heavy-duty transmission of  FIG. 2 ; 
           [0044]      FIG. 19  is a cross-sectional view showing a 5 th  range power path of the heavy-duty transmission of  FIG. 2 ; 
           [0045]      FIG. 20  is a cross-sectional view showing a 6 th  range power path of the heavy-duty transmission of  FIG. 2 ; 
           [0046]      FIG. 21  is a cross-sectional view showing a 7 th  range power path of the heavy-duty transmission of  FIG. 2 ; 
           [0047]      FIG. 22  is a cross-sectional view showing an 8 th  range power path of the heavy-duty transmission of  FIG. 2 ; 
           [0048]      FIG. 23  is a cross-sectional view showing a 9 th  range power path of the heavy-duty transmission of  FIG. 2 ; and 
           [0049]      FIG. 24  is a simplified schematic view of a component layout of a variant of the heavy-duty transmission of  FIG. 2 . 
       
    
    
       [0050]    In describing preferred embodiments of the invention, which are illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific terms so selected and it is to be understood that each specific term includes all technical equivalents, which operate in a similar manner to accomplish a similar purpose. For example, the words “connected”, “attached”, “coupled”, or terms similar thereto are often used. They are not limited to direct connection but include connection through other elements where such connection is recognized as being equivalent by those skilled in the art. 
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0051]    Referring to  FIG. 1 , a heavy-duty industrial transmission  5  is shown implemented at each of multiple fracturing pump (“frac pump”) systems  8  at a drilling site  10 . Drilling site  10  is schematically shown set up for hydraulic fracturing (“fracking”) subterranean formations to stimulate a well with a borehole  12  that extends downwardly from a wellhead  14 . A fracturing fluid (“frac fluid”) storage system  16  is configured to deliver frac fluid  18  through outlet line  20  into inlet lines  22  of the frac pump systems  8 . Frac site control system  26  communicates with and is configured to control each of the frac pump systems  8 . Frac site control system  26  includes a computer that executes various stored programs while receiving inputs from and sending commands to the frac pump systems  8  for controlling, for example, activation or selectively bringing the frac pump systems  8  online for fracking the subterranean formations by controlling the various electronic, electromechanical, and hydraulic systems and/or other components of each frac pump system  8 . Frac site control system  26  may include the TDEC-500 electronic control system available from Twin Disc®, Inc. for controlling the frac pump systems  8 . Frac pump systems  8  that are activated and online deliver frac fluid  18  under high pressure, for example, 10,000 psi or more through frac pump system outlet lines  28  into manifold  30  that delivers the pressurized frac fluid  18  through manifold outlet line  32  and wellhead  14  to flow through borehole  12  into the well for fracturing the subterranean formation. 
         [0052]    Still referring to  FIG. 1 , each frac pump system  8  is shown mounted to a trailer  34  that can be towed by a tractor or tow vehicle, such as semi-tractor  36 . To pressurize the frac fluid  18 , each frac pump system  8  includes a high horsepower engine shown as engine  38  that can be a diesel or other internal combustion engine capable of outputting at least about 1,000 hp, for example, about 2,500 hp or more. Torque converter  40  connects engine  38  to a heavy-duty transmission shown as transmission  5  that is rated to handle the power from the engine  38 . Transmission  5  is connected to drive a heavy-duty frac pump, shown as pump  44 , that is capable of highly pressurizing frac fluid  18 , for example, to a pressure of at least about 10,000 psi. 
         [0053]    Referring now to  FIGS. 2 and 3 , torque converter  40  is housed in converter housing  46  that is connected to transmission housing  48  at an input end  50  of transmission housing  48  that is opposite an output end  52 . A sump  54  is connected to and extends from a bottom portion of transmission housing  48  and holds oil used for lubrication and hydraulic component actuation for torque converter  40  and transmission  5 . Transmission control system  56  controls the component actuation for torque converter  40  and transmission  5 . Transmission control system  56  includes transmission controller  58  that cooperatively communicates with and is controlled by frac site control system  26 . Transmission controller  58  includes a computer that executes various stored programs while receiving inputs from and sending commands to various components, such as torque converter solenoid packs  60  and transmission solenoid packs  62 , to control oil flow and engage/disengage various clutches to activate a lockup clutch of torque converter  40  and also to select distinct power paths through and change ranges of transmission  5 , as explained in greater detail elsewhere herein. 
         [0054]    Referring now to  FIG. 4 , transmission  5  is configured with a four-stage planetary arrangement  64  that provides nine ranges without reversing action or reverse gear(s) so the output shaft  72  may be arranged to rotate in only a single direction and without (a) countershaft(s). The ranges provide deep reduction ratios at the low range(s) and consistent steps between ranges. The below Table 1 shows an exemplary set of nine ranges of transmission  5 , showing the reduction ratio for each of the ranges. Of the nine ranges represented in Table 1, 2 nd  range through 9 th  range each has a ratio step of about an 80% reduction of its preceding range reduction ratio, with each shift or range change to a higher range providing a subsequent reduction ratio of between about 77% and about 83% of that of its preceding range until obtaining a direct drive ratio or reduction ratio of 1.00 in 9 th  range. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Range 
                 Reduction Ratio 
               
               
                   
                   
               
             
             
               
                   
                 1 
                 5.776 
               
               
                   
                 2 
                 4.763 
               
               
                   
                 3 
                 3.673 
               
               
                   
                 4 
                 3.033 
               
               
                   
                 5 
                 2.501 
               
               
                   
                 6 
                 1.929 
               
               
                   
                 7 
                 1.572 
               
               
                   
                 8 
                 1.297 
               
               
                   
                 9 
                 1.000 
               
               
                   
                   
               
             
          
         
       
     
         [0055]    Still referring to  FIG. 4 , four-stage planetary arrangement  64  is concentrically arranged outwardly of multiple longitudinally aligned shafts of transmission  5  that receive power from torque converter output shaft  66 . The multiple longitudinally aligned shafts of transmission  5  include transmission input shaft  68 , transmission center shaft  70 , and transmission output shaft  72 . The transmission input, center, and output shafts  68 ,  70 ,  72  are coupled to each other through the four-stage planetary arrangement  64  to establish the reduction ratios in the different ranges between the rotational speeds of the transmission input and output shafts  68 ,  72 . 
         [0056]    Still referring to  FIG. 4 , four-stage planetary arrangement  64  includes front planetary section  74  at the input end  50  and back planetary section  76  at the output end  52  within transmission housing  48 . Front planetary section  74  includes a pair of front planetary gearsets, shown as planetary gearsets P 1 , P 2 , that are configured to selectively deliver power along different power paths from input shaft  68  to center shaft  70 . Back planetary section  76  includes a pair of back planetary gearsets, shown as planetary gearsets P 3 , P 4 , that are configured to selectively deliver power along different power paths from center shaft  70  to output shaft  72 . 
         [0057]    Referring now to  FIG. 5 , planetary gearset P 1  includes sun gear  82  with external teeth that mesh with external teeth of planet gears  84  that are supported by planet carrier  86 . The teeth of planet gears  84  of a first set of planet gears also mesh with internal teeth of ring gear  88  of the planetary gearset P 1 . Planetary gearset P 2  includes sun gear  92  with external teeth that mesh with external teeth of planet gears  94  that are supported by planet carrier  96 . The teeth of planet gears  94  of a second set of planet gears also mesh with internal teeth of ring gear  98  of the planetary gearset P 2 . Planetary gearset P 3  includes sun gear  102  with external teeth that mesh with external teeth of planet gears  104  of a third set of planet gears that are supported by planet carrier  106 . The teeth of planet gears  104  also mesh with internal teeth of ring gear  108  of the planetary gearset P 3 . Planetary gearset P 4  includes sun gear  112  with external teeth that mesh with external teeth of planet gears  114  of a fourth set of planet gears that are supported by planet carrier  116 . The teeth of planet gears  114  also mesh with internal teeth of ring gear  118  of the planetary gearset P 4 . 
         [0058]    Still referring to  FIG. 5 , at the front planetary section  74 , the planet carriers  86 ,  96  of planetary gearsets P 1 , P 2  are connected to each other through carrier adapter drum  120  to always rotate at the same speed, defining a common planet carrier assembly in the front planetary section  74 . Ring gears  88 ,  98  of planetary gearsets P 1 , P 2  are arranged in a space that is surrounded by an enclosure defined by the carrier adapter drum  120 . Ring gears  88 ,  98  of planetary gearsets P 1 , P 2  are connected to each other through ring gear collar  122  to always rotate in unison and thus at the same speed, defining a common ring gear in the front planetary section  74 . Ring gear adapter flange  124  is internally splined to external splines of input shaft  68  and connected to ring gear collar  122  so that ring gears  88 ,  98  of planetary gearsets P 1 , P 2  always rotate with input shaft  68 , either as transmitting power or as back-driven. 
         [0059]    Still referring to  FIG. 5 , at the back planetary section  76 , sun gear  112  of planetary gearset P 4  includes sun gear collar  126  that is internally splined to center shaft  70 . Sun gear  102  of planetary gearset P 3  is internally splined to external splines of collar  126  so that sun gears  102 ,  112  of planetary gearsets P 3 , P 4  always rotate with center shaft  70 , either as transmitting power or as back-driven. Planet carrier  106  of planetary gearset P 3  is connected to ring gear  118  of planetary gearset P 4  through carrier/ring adapter collar  128  to always rotate at the same speed. Ring gears  108  and  118  of planetary gearsets P 3  and P 4  are separate from and axially aligned with each other and can rotate at different speeds. 
         [0060]    Still referring to  FIG. 5 , four-stage planetary arrangement  64  has various clutches that are controlled by transmission control system  56  ( FIGS. 2 and 3 ) to provide the nine ranges of transmission  5 , such as by controlling oil flow to engage/disengage the clutches to select distinct power paths through the planetary gearsets P 1 , P 2  of front planetary section  74  and through the planetary gearsets P 3 , P 4  of back planetary section  76 . At the front planetary section  74 , three clutches are shown as clutches C 1 , C 2 , C 3  as a front set of clutches. At the back planetary section  76 , three clutches are shown as clutches C 4 , C 5 , C 6  as a back set of clutches. The clutches C 1 , C 2 , C 3 , C 4 , C 5 , C 6  may be balancing clutches or stationary clutches and are all shown as piston-actuated multi-disc clutches that have interleaved clutch discs and friction discs with respective internal and external teeth or tangs that engage corresponding components to engage and selectively lock components with respect to other components or disengage and allow free rotation between the corresponding components. 
         [0061]    Still referring to  FIG. 5 , at the front planetary section  74 , clutch C 1  is configured to selectively ground the sun gear  82  of planetary gearset P 1 . Sun gear  82  of planetary gearset P 1  includes a collar  130  that is externally splined to internal splines of a clutch backplate  132 . Clutch backplate  132  has an upper outer end  134  connected to clutch C 1  so that engaging clutch C 1  grounds sun gear  82  by stopping rotation of clutch backplate  132  and sun gear  82  with respect to the transmission housing  48 . Clutch C 2  is configured to selectively lock the sun gear  82  of planetary gearset P 1  to input shaft  68 . Clutch backplate  132  has an intermediate segment  136  connected to clutch C 2  so that engaging clutch C 2  locks sun gear  82  into rotational unison with input shaft  68  through input shaft lock collar  138  that is internally splined to external splines of input shaft  68  and is connected to clutch C 2 . Engaging clutch C 2  to lock sun gear  82  into rotational unison with input shaft  68  locks up the front planetary section  74  so all of the components in the planetary gearsets P 1 , P 2  rotate as a unit with the planet gears  84 ,  94  traveling with their carriers  86 ,  86 , without rotating about their own axes. This provides a 1:1 gear ratio with no reduction through the front planetary section  74  when clutch C 2  is engaged. Clutch C 3  is configured to selectively ground the sun gear  92  of planetary gearset P 2 . Sun gear  92  of planetary gearset P 2  is internally splined to external splines of an inner segment of ground flange  140 . Engaging clutch C 3  grounds sun gear  92  by stopping rotation of ground flange  140  and the sun gear  92  with respect to the transmission housing  48 . 
         [0062]    Still referring to  FIG. 5 , at the back planetary section  76 , clutch C 4  is configured to selectively lock carrier  106  of planetary gearset P 3  into rotational unison with center shaft  70 . This is done through sun gear collar  142  that extends from sun gear  102  of planetary gearset P 3  and is connected to clutch C 4  that is also connected to carrier  106  of the planetary gearset P 3 . Engaging clutch C 4  to lock the carrier  106  to rotate with center shaft  70  through sun gear  102  of planetary gearset P 3  and sun gear collar  126  of planetary gearset P 4  causes all of the components in the planetary gearsets P 3 , P 4  to rotate as a unit with the planet gears  104 ,  114  traveling with their carriers  106 ,  116  without rotating about their own axes. This locks up the back planetary section  76  when clutch C 4  is engaged and provides a 1:1 gear ratio with no reduction through the back planetary section  76 . Clutch C 5  is configured to selectively ground the ring gear  108  of planetary gearset P 3 . An outer surface of ring gear  108  is connected to clutch C 5  so that engaging clutch C 5  grounds ring gear  108  by stopping rotation of ring gear  108  with respect to transmission housing  48 . Clutch C 6  is configured to selectively ground the ring gear  118  of planetary gearset P 4  and the planet carrier  106  of planetary gearset P 3 . An outer surface of ring gear  118  is connected to clutch C 6  so that engaging clutch C 6  grounds ring gear  118  and carrier  106  by stopping rotation of ring gear  118  with respect to transmission housing  48  and also stopping rotation of carrier  106  that is connected to ring gear  118  by carrier/ring adapter collar  128 . 
         [0063]    To select each of the nine ranges of transmission  5 , transmission control system  56  controls the four-stage planetary arrangement  64  to engage a single one of the clutches C 1 , C 2 , C 3  of the front planetary section  74  and a single one of the clutches C 4 , C 5 , C 6  of the back planetary section  76 . Transmission control system  56  performs a shift methodology that primarily uses single pack shift events to minimize multipack shift events. During each single pack shift event, transmission control system  56  changes engagement status or state of one of the clutches C 1 , C 2 , C 3 , C 4 , C 5 , C 6  to disengage one previously engaged clutch C 1 , C 2 , C 3 , C 4 , C 5 , C 6  and engage one newly engaged clutch C 1 , C 2 , C 3 , C 4 , C 5 , C 6 . 
         [0064]    Referring generally now to  FIGS. 6-23 , power paths are shown through the transmission  5  for the different ranges that provide the reduction ratios in the above Table 1, which are established by the selective engagement and disengagements of the various clutches C 1 , C 2 , C 3 , C 4 , C 5 , C 6  of the four-stage planetary arrangement  64 . As explained in greater detail elsewhere herein, more than half of the shift events to change ranges are done by way of single pack shift events, shown here as six single pack shift events that are used in the shifting methodology of transmission  5 . The single pack shift events correspond to changing from 1″ range to 2 nd  range, from 2 nd  range to 3 rd  range, from 4 th  range to 5 th  range, from 5 th  range to 6 th  range, from 7 th  range to 8 th  range, and from 8 th  range to 9 th  range. Two multipack shift events are used in the shifting methodology of transmission  5 . The multipack shift events correspond to changing from 3 rd  range to 4 th  range and from 6 th  range to 7 th  range. 
         [0065]    Still referring generally to  FIGS. 6-23 , simplified schematic representations or stick diagrams of the power paths are shown in  FIGS. 6-14 . In  FIGS. 6-14 , the power path, defined by the path along which torque is transmitted through the respective components of the four-stage planetary arrangement  64  to translate rotation of transmission input shaft  68  into rotation of transmission output shaft  72 , is shown with solid black lines. Back-driven components that rotate but did not transmit torque are shown with long-dashed lines. Grounded components that are held stationary are shown with short-dashed lines. In  FIGS. 15-23 , the power path is shown by the components that are loosely-stippled. Grounded components that are held stationary are shown tightly-stippled. 
         [0066]      FIGS. 6 and 15  show the power path through transmission  5  in 1 st  range. In 1st range, in the front planetary section  74 , clutch C 3  is engaged, which grounds sun gear  92  of planetary gearset P 2 . Power flows from input shaft  68  through ring gear adapter flange  124  and ring gear  98  of planetary gearset P 2  that rotates the planet gears  94  to drive the carriers  86 ,  96  into rotation, which delivers power out of the carrier  96  to rotate and deliver power to center shaft  70 . As shown in  FIG. 6 , sun gear  82 , planet gears  84 , planet carrier  86 , ring gear  88 , and the portion of carrier  96  upstream of planets  94  are back-driven to rotate without seeing power or transferring driving torque of transmission  5 . Referring again to  FIGS. 6 and 15 , power enters the back planetary section  76  through center shaft  70 . In the back planetary section  76 , clutch C 5  remains disengaged and sun gear  102 , planet gears  104 , and ring gear  108  are back-driven to rotate without seeing power or transferring driving torque of transmission  5 . Clutch C 6  is engaged, which grounds ring gear  118  of planetary gearset P 4  and planet carrier  106  of planetary gearset P 3 . Power flows from the center shaft  70  through sun gear  112  on planetary gearset P 4  that rotates the planet gears  114  to drive the carrier  116  into rotation, which delivers power out of the carrier  116  to rotate and deliver power to output shaft  72 . 
         [0067]      FIGS. 7 and 16  show the power path through transmission  5  in 2 nd  range, following a single pack shift event that shifts transmission  5  from 1 st  range to 2 nd  range. In 2 nd  range, in the front planetary section  74 , clutch C 1  is engaged, which grounds sun gear  82  of planetary gearset P 1 . Power flows from input shaft  68  through ring gear adapter flange  124  and ring gear  88  of planetary gearset P 1  that rotates the planet gears  84  to drive the carriers  86  and  96  into rotation, which delivers power out of the carrier  96  to rotate and deliver power to center shaft  70 . As shown in  FIG. 7 , sun gear  92 , planet gears  94 , and ring gear  98  planetary gearset P 2  are back-driven to rotate without seeing power or transferring driving torque of transmission  5 . Referring again to  FIGS. 7 and 16 , in the back planetary section  76 , clutch C 6  remains engaged and power flows through the back planetary section  76  along the same power flow path as when the transmission  5  is in 1 st  range as described above with respect to  FIGS. 6 and 15 . 
         [0068]      FIGS. 8 and 17  show the power path through transmission  5  in 3 rd  range, following a single pack shift event that shifts transmission  5  from 2 nd  range to 3 rd  range. In 3 rd  range, in the front planetary section  74 , clutch C 2  is engaged, which locks sun gear  82  of planetary gearset P 1  to rotate in unison with input shaft  68 . This locks up the front planetary section  74  so all of the components of planetary gearsets P 1 , P 2  rotate as a unit, with the planet gears  84 ,  94  not rotating about their own axes. Power flows from input shaft  68  through sun gear  82  and ring gear adapter flange  124 , through the carriers  86 ,  96 , and out carrier  96  to center shaft  70  without a reduction and thus a 1:1 gear ratio at the front planetary section  74 , which rotates center shaft  70  the same speed as input shaft  68 . As shown in  FIG. 8 , sun gear  92 , planet gears  94 , and ring gear  98  planetary gearset P 2  are back-driven to rotate without seeing power or transferring driving torque of transmission  5 . Referring again to  FIGS. 8 and 17 , in the back planetary section  76 , clutch C 6  remains engaged and power flows through the back planetary section  76  along the same powerful path as when the transmission  5  is in 1 st  range as described above with respect to  FIGS. 6 and 15 . 
         [0069]      FIGS. 9 and 18  show the power path through transmission  5  in 4 th  range, following a double pack shift as a multipack shift event that shifts transmission  5  from 3 rd  range to 4 th  range. In 4 th  range, in the front planetary section  74 , clutch C 3  is again engaged, and power flows through the front planetary section  74  along the same powerful path as when the transmission  5  is in 1 st  range as described above with respect to  FIGS. 6 and 15 . In the back planetary section  76 , clutch C 5  is engaged, which grounds ring gear  108  of planetary gearset P 3 . Power flows from the center shaft  70  through sun gears  102 ,  112  of planetary gearsets P 3 , P 4  that rotates the planet gears  104 ,  114  to drive the carrier  106  and ring gear  118  into rotation, which delivers power out of the carrier  116  to rotate and deliver power to output shaft  72 . 
         [0070]      FIGS. 10 and 19  show the power path through transmission  5  in 5 th  range, following a single pack shift event that shifts transmission  5  from 4 th  range to 5th range. In 5 th  range, in the front planetary section  74 , clutch C 1  is again engaged, and power flows through the front planetary section  74  along the same powerful path as when the transmission  5  is in 2 nd  range as described above with respect to  FIGS. 7 and 16 . In the back planetary section  76 , clutch C 5  remains engaged, and power flows through the back planetary section  76  along the same powerful path as when the transmission  5  is in 4 th  range as described above with respect to  FIGS. 9 and 18 . 
         [0071]      FIGS. 11 and 20  show the power path through transmission  5  in 6 th  range, following a single pack shift event that shifts transmission  5  from 5 th  range to 6 th  range. In 6 th  range, in the front planetary section  74 , clutch C 2  is again engaged to lock up the front planetary section  74  without reduction, and power flows through the front planetary section  74  along the same powerful path as when the transmission  5  is in 3 rd  range as described above with respect to  FIGS. 8 and 17 . In the back planetary section  76 , clutch C 5  remains engaged, and power flows through the back planetary section  76  along the same powerful path as when the transmission  5  is in 4 th  range as described above with respect to  FIGS. 9 and 18 . 
         [0072]      FIGS. 12 and 21  show the power path through transmission  5  in 7 th  range, following a double pack shift as a multipack shift event that shifts transmission  5  from 6 th  range to 7 th  range. In 7 th  range, in the front planetary section  74 , clutch C 3  is again engaged, and power flows through the front planetary section  74  along the same power path as when the transmission  5  is in 1 st  range as described above with respect to  FIGS. 6 and 15 . In the back planetary section  76 , clutch C 4  is engaged, which locks carrier  106  of planetary gearset P 3  to rotate in unison with center shaft  70 . This locks up the back planetary section  76  so all of the components of planetary gearsets P 3 , P 4  rotate as a unit, with the planet gears  104 ,  114  not rotating about their own axes. Power flows from center shaft  70  through carrier  106  and sun gear  112  and ring gear  118  and out carrier  116  to output shaft  72  without a reduction and thus a 1:1 gear ratio at the back planetary section  76  to rotate output shaft  72  at the same speed as center shaft  70 . 
         [0073]      FIGS. 13 and 22  show the power path through transmission  5  in 8 th  range, following a single pack shift event that shifts transmission  5  from 7 th  range to 8 th  range. In 8 th  range, in the front planetary section  74 , clutch C 1  is again engaged and, power flows through the front planetary section  74  along the same power path as when the transmission  5  is in 2 nd  range as described above with respect to  FIGS. 7 and 16 . In the back planetary section  76 , clutch C 4  remains engaged to lock up the back planetary section  76  without reduction, and power flows through the back planetary section  76  along the same power path as when the transmission  5  is in 7 th  range as described above with respect to  FIGS. 12 and 21 . 
         [0074]      FIGS. 14 and 22  show the power path through transmission  5  in 9 th  range, following a single pack shift event that shifts transmission  5  from 8 th  range to 9th range. In 9 th  range, in the front planetary section  74 , clutch C 2  is again engaged to lock up the front planetary section  74  without reduction, and power flows through the front planetary section  74  along the same power path as when the transmission  5  is in 3 rd  range, as described above with respect to  FIGS. 8 and 17 . In the back planetary section  76 , clutch C 4  remains engaged to lock up the back planetary section  76  without reduction, and power flows through the back planetary section  76  along the same power path as when the transmission  5  is in 7 th  range, as described above with respect to  FIGS. 12 and 21 . This provides the overall 1:1 gear ratio without reduction shown in Table 1 above when the transmission  5  is in 9 th  range. 
         [0075]    Referring now to  FIG. 24 , this stick diagram schematically shows a four-stage planetary arrangement  64  that has the same back planetary section  76  as that shown in  FIGS. 5-23 , with a variation of the front planetary section  74  compared to that in  FIGS. 5-23 . In the front planetary section  74  shown in  FIG. 24 , the planetary carrier  86  of planetary gearset P 1  is connected to ring gear  98  of planetary gearset P 2 . Ring gear  88  of planetary gearset P 1  is connected to planet carrier  96  of planetary gearset P 2 . In this arrangement, the largest or deepest reduction is achieved by engaging clutch C 3  to ground the sun gear  92  of planetary gearset P 2 . This provides a power path in which power drives from input shaft  68  into ring gear  98  of planetary gearset P 2  and outputs through planet carrier  96  planetary gearset P 2  and output speed that rotates center shaft  70  at a slower speed than the input speed of input shaft  68 . Engaging clutch C 2  locks sun gear  82  of planetary gearset P 1  into rotational unison with input shaft  68 , which may include locking sun gear  82  to planet carrier  86  of planetary gearset P 1 , to lock up the front planetary section  74 . When the front planetary section  74  is locked up, all components in front planetary section  74  rotate at the same speed with the planet gears  84 ,  94  traveling with their carriers  86 ,  86 , without rotating about their own axes to provide a 1:1 gear ratio with no reduction. Engaging clutch C 1  grounds sun gear  82  of planetary gearset P 1 . This provides a power path in which power drives from input shaft  68  into planet carrier  86  of planetary gearset P 1  and outputs through planetary ring gear  88  of planetary gearset P 1  at a speed greater than input speed, which rotates center shaft  70  at a faster speed than the input speed of input shaft  68 . 
         [0076]    Although the best mode contemplated by the inventors of carrying out the present invention is disclosed above, practice of the above invention is not limited thereto. It will be manifest that various additions, modifications, and rearrangements of the features of the present invention may be made without deviating from the spirit and the scope of the underlying inventive concept.