Abstract:
The apparatus is a 28 speed, two section, transmission that requires only a single clutch swap for most changeovers between adjacent ratios. It uses a first section with three close ratio forward speeds and one reverse along with a second section that is an 11 speed, wide ratio, transmission. The two transmission sections are arranged in series resulting at least 28 usable forward speeds. The second section includes an intermediate planetary gear set without a ring gear and an output planetary gear set that is a conventional simple planetary gear set with a two sun gears, two planes of planetary gears on a single carrier, and two ring gears.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention deals generally with mechanical transmissions and more specifically with a power shift transmission with a large number of forward ratios and very smooth shifts between gear ratios.  
         [0002]     Power shift transmissions have been in use for agricultural tractors for about 40 years. Such transmissions now provide the capability of shifting through all the forward gears while moving and while under load without using a clutch pedal. The only action required by an operator is the selection of the desired gear. The actual changeover, including the operation of one or more clutches is electronically controlled and performed by hydraulically powered clutches.  
         [0003]     In order to provide a wide range of ratios divided into a large number of small forward ratio steps in a transmission of practical size and reasonable cost, such transmissions are actually built as two or three transmissions in a series arrangement. Such a transmission is disclosed in U.S. Pat. No. 5,036,718 issued to Bulgrien. However, in such transmissions some of the shifts between adjacent gear ratios require complex simultaneous changeovers in two or three of the transmissions. These complex changeovers frequently result in jerky shifts. Moreover, the tendency to increase the spread of the overall ratio over the years has increased the number and severity of these difficult shifts.  
         [0004]     For example, considering only forward speeds, the 18 speed tractor transmission mentioned above is constructed with an first section having a three speed transmission with approximately 1.17 ratio steps. The first section is followed by a middle section that is a three speed transmission with ratio steps of approximately 1.6 and then an output section that is a two speed transmission with a 4.1 ratio step. First gear is achieved by using the lowest ratio in each of the three transmission sections. Second and third gears are then achieved by shifting only the input section while leaving the lowest ratio selected in the middle and output sections. When shifting from 3 rd  to 4 th  gear, the middle section is shifted from its lowest ratio to its intermediate ratio while the input section is shifted from its highest ratio to its lowest ratio. This multiple changeover pattern continues through all of the ratio combinations to yield the 18 different gear ratios.  
         [0005]     However, such a transmission causes discontinuities in the vehicle motion, the so called jerky shifts, when one or more sections are being upshifted while another is being shifted down. Each individual shift involves clutch action that engages one clutch and gear set and disengages another. Such changeovers are referred to in the industry as “clutch swaps”. The multiple gear changes are then referred to as “double swaps” and “triple swaps” as each section of the transmission is shifted by “swapping” clutches, that is, releasing one clutch and applying another. Shifting two sections thus involves two clutch changeovers, a double swap, and shifting all three sections involves three changeovers, a triple swap.  
         [0006]     The worst condition for the transmission described above occurs when making the triple swap required to downshift from 10 th  to 9 th  gear while under load. To accomplish this shift, the input and middle sections are both shifted from their lowest ratios to their highest ratios while the output section is shifted from its high ratio to is low ratio. To make this shift with minimal change in ground speed would require setting the pressure in the high ratio clutch in the output section to a level that is just sufficient to transmit the torque required by the load, then shifting the input and middle sections to bring up the speed of the intermediate gears and shafts, then completing the shift to the low ratio clutch in the output section. To do this the engine and flywheel would have to momentarily provide enough torque to pull a 10 th  gear load in 18 th  gear while the intermediate gears and shafts accelerate. 18 th  gear is about 3.5 times faster than 10 th  gear. In fact, the clutches in the input and middle sections do not have sufficient torque capacity to do this, and even if they did the loss in engine speed would be severe. To complete the shift without coming to a complete stop and without excessive loss of engine speed, the output speed is allowed to drop rapidly for a brief time while the intermediate gears and shafts accelerate. It is this action that causes a jerky shift.  
         [0007]     The ratio change in the transmission sections that are shifted up during an overall downshift is a good indicator of the difficulty in making shifts involving multiple clutch swaps. In the transmission described above, the shift from 7 th  to 6 th  gear can be made quite smoothly. This shift requires shifting the input section from its lowest ratio to its highest ratio while shifting the middle section from its highest ratio to its intermediate ratio. To make this shift with minimal change in output speed requires effectively momentarily pulling a 7 th  gear load in 9 th  gear. The ratio between 7 th  gear and 9 th  gear is only about 1.37 compared to the ratio of 3.5 between 1 oth gear and 18 th  gear discussed in the example above, so the downshift from 7 th  gear to 6 th  gear is much smoother and less difficult than the shift from 10 th  gear to 9 th  gear.  
         [0008]     One very beneficial solution would be to have a power shift transmission in which all shifts between adjacent gears were accomplished with single clutch swaps as described in U.S. Pat. No. 6,190,280 to Horsch, because this would theoretically provides smooth shifts going both up and down. However, the Horsch transmission has rather uneven ratio steps and this condition is further aggravated if the overall ratio range is increased.  
       SUMMARY OF THE INVENTION  
       [0009]     The preferred embodiment of the present invention provides a two section power shift transmission that requires only a single clutch swap for most changeovers between adjacent ratios, and uses double swaps for only a few changeovers. No triple swaps are required. Many of the resulting forward ratios are in near geometric progression. For example, in the preferred embodiment in most cases shifting down one speed results in an increase in the gear ratio of about 13 percent.  
         [0010]     This is accomplished by the use of a first section with three close ratio forward speeds and one reverse along with a second output section that is an 11 speed, wide ratio, transmission section. The two transmission sections are arranged in series resulting in 33 forward ratios and 11 reverse ratios. Although some of the ratios produced are nearly duplicates of others, skipping these duplicate ratios still yields at least 28 usable forward speeds.  
         [0011]     The invention produces a nearly geometric progression of the ratios, but, because of the required double clutch swaps for some of the shifts, with a slight compromise of shift quality. For the present invention, the most difficult downshifts involve shifting the 3 speed section up from 1 st  to 3 rd  while downshifting the 11 speed section. However, due to the small ratio steps, this only involves about a 1.28 to 1 speed increase from the input section. This is a great improvement over all current and previous power shift transmissions on the market.  
         [0012]     Among the advantages of the present invention are its elimination of the difficult shifts which have previously been inherent in all full power shift tractor transmissions and its small ratio steps that approximately match the smallest ratio steps currently available. Furthermore, the present invention&#39;s  33  ratios and 28 forward speeds provides a wider overall ratio spread and more forward speeds than any power shift transmissions currently available. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a schematic diagram of the transmission of the preferred embodiment of the invention.  
         [0014]      FIG. 2  is a chart showing the gear sequences and clutch combinations attainable with the transmission shown in the schematic diagram of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]      FIG. 1  is a schematic diagram of transmission  10  of the preferred embodiment of the invention in which each of the ten clutches is identified by the designation C 1  through C 10  located adjacent to the symbol for the clutch, shafts are identified adjacent to their symbols, and gears are identified by numerals preceded by the letter G and identifying lines. It should also be understood that the clutches are all pictured in a vertical orientation and labeled near both ends for clarity. On the other hand, although all gears are also pictured in a vertical orientation and have two ends, they are typically labeled only once. The number of teeth in each gear of the preferred embodiment is indicated by the number adjacent to the symbol representing the gear in  FIG. 1 . Furthermore, the relative size relationship of gear diameters is also shown in  FIG. 1 . That is, larger gears are shown larger and smaller gears are shown relatively smaller. Moreover, where possible, driver and driven gears are shown adjacent to each other, but where they are not drawn adjacent to each other, their relationship is explained in the text.  
         [0016]      FIG. 1  is divided into a first section and a second section. The first section includes input shaft  1 , three clutches C 1 , C 2 , and C 3  driven directly from input shaft I, clutch  10  for reverse, several gears driven directly by these clutches, and shaft C. The second section includes shaft A, clutches C 4  and C 5  and their associated gears, planetary gear set  12 , planetary gear set  14  and output shaft O.  
         [0017]     Power from the engine (not shown) is delivered to transmission  10  at input shaft I, and shaft I also functions as shaft P, the power takeoff (PTO) shaft. The PTO shaft delivers power to a conventional hydraulic system (not shown) which ultimately furnishes the power for the operation of all the clutches described.  
         [0018]     Input shaft I also is attached to and drives clutches C 1 , C 2 , and C 3 , and by means of gear G 1 , it also drives C 10  (the reverse clutch). Selections are made from these clutches to drive the rest of transmission  10 . The operation of  FIG. 1  will be more easily followed by the simultaneous use of the gear sequence chart of  FIG. 2 .  
         [0019]     The gear sequence chart of  FIG. 2  lists the highest gear ratio at the top of the chart and the lowest gear ratio at the bottom, with the entire sequence progressing between the highest and lowest gears. Lines that are not numbered in the “Gear” column have small numerals to indicate that these gear ratios are not recommended for use because they are too close to other ratios which have been selected. The columns of  FIG. 2  are labeled as noted, and they provide the information indicated below for each horizontal line.  
         [0020]     Col. “Gear” identifies the gear selection within the sequence for the line.  
         [0021]     Col. 2 indicates the gear selection within the second section of the transmission with a number and the gear selection within the first section with L (low), M (medium), or H (high) for the line.  
         [0022]     Col. “Ratio” shows the actual gear ratio for the gear selection.  
         [0023]     Col. “1/Ratio” gives the inverse of the gear ratio, a number used for design criteria.  
         [0024]     Col. “Clutches” shows the clutches shown in  FIG. 1  that are engaged for the gear selection.  
         [0025]     Col. “Swaps” shows the number of clutch swaps required to change between the gear selections immediately above and below the line.  
         [0026]     Col. “Step” indicates the change in ratio between the gear selections immediately above and below the line.  
         [0027]     Col. “mph” tells the ground speed for the gear selection in miles per hour.  
         [0028]     Col. “km/h” tells the ground speed for the gear in kilometers per hour.  
         [0029]     Col. “R step” indicates the change in ratio for reverse speeds.  
         [0030]     Col. “R mph” tells the ground speed in reverse in miles per hour.  
         [0031]     Col. “R km/h” tells the ground speed in reverse in kilometers per hour.  
         [0032]     It should be noted that, for reverse speeds in the chart of  FIG. 2 , gear selections for ground speeds over 12 mph and one lower speed at gear selection  12  are not actually used, although they are theoretically available. As with the other unused gear selections, these lines are printed with smaller numerals.  
         [0033]     Several gear selections are described below with reference to  FIG. 1 , beginning with gear selection  1 , at the bottom line of  FIG. 2 .  
         [0034]     Gear selection  1  produces a ground speed of only 1.33 mph, and for it clutches C 1 , C 4 , and C 6  are engaged. Clutch C 1  is connected to gear G 1  that is permanently attached to input shaft I so that gear G 1  is constantly rotating. The engagement of clutch C 1  causes gear G 2  to rotate, and gear G 2  drives gear G 3  that is attached to shaft C. Shaft C then drives shaft A through gears G 4  and G 5 . In fact, gears G 4  and G 5  always drive shaft A from shaft C so that the speed of shaft A is determined by the selection of either clutch C 1 , C 2 , C 3 , or C 10  (reverse) that interconnect shaft I to shaft C with different size gears.  
         [0035]     Therefore, there are three forward and one reverse speed choices available between shaft I and shaft C. There are three forward gear combinations, G 2  to G 3 , G 6  to G 4 , and G 7  to G 8  that connect shaft I and shaft C depending upon the selection of clutches C 1 , C 2 , or C 3 . In the preferred embodiment of the invention, theses gear combinations are designed to yield gear ratio steps of 1.13 as the engaged clutch is sequenced from C 1  to C 2  to C 3 .  
         [0036]     For clarification, it should be understood that gear G 15 , which is the gear powered from reverse clutch C 10 , actually engages gear G 3 , although they are not shown in contact in  FIG. 1 . Reverse clutch thereby also interconnects shaft I with shaft C, but, of course, with reverse rotation.  
         [0037]     Clutches C 4  and C 5  then provide the choice of two gear sets with different ratios, G 9  to G 10  and G 11  to G 12 , by which to drive planetary gear carrier CR 1  and sun gear G 20  from shaft A. For gear selection  1  of  FIG. 2 , clutch C 4  is engaged to rotate sun gear G 20 . In gear selection  1  of  FIG. 2 , clutch C 6  is also engaged. This stops ring gear RG 1  of output planetary gear set  14  and causes output carrier CR 2  to rotate at a slower rate than sun gear G 20 . Output shaft O, which is attached to output carrier CR 2  is thereby driven from shaft A through the planetary reduction of output planetary gear set  14 .  
         [0038]     It should be understood that intermediate planetary gear set  12  is constructed without a ring gear to accomplish its required operation while output planetary gear set  14  consists of two conventional simple planetary gear sets with two sun gears, two planes of planetary gears mounted on a single carrier, and two ring gears.  
         [0039]     The three lowest gear selections of  FIG. 2  are accomplished by merely swapping through clutches C 1 , C 2 , and C 3 .  
         [0040]     Another example taken from  FIG. 2  is the series of steps from gear selection  16  through gear selection  24 . This sequence starts at gear selection  16  with clutches C 1 , C 4 , and C 8  engaged. Clutch C 8  directly connects output carrier CR 2  and output shaft O to intermediate carrier CR 1 , so that clutch C 1  and C 4  determine the speed of output shaft O. Gear selections  17  and  18  then swap clutch C 1  to C 2  and then to C 3 , thus increasing the gear ratio by 1.13 with each step.  
         [0041]     For gear selection  19  there is a double swap when clutch C 3  is exchanged for clutch C 1  for a lower gear ratio while clutch C 4  is exchanged for clutch C 5  for a higher gear ratio. The net change in ratio with these two swaps is 1.13, essentially the same as the last two steps. The next two gear selections merely require once more moving from clutch C 1  to clutches C 2  and C 3 , each with a ratio change of 1.13.  
         [0042]     Then for gear selection  22 , there is another double swap. Clutch C 3  is again exchanged for clutch C 1  and clutch  5  is exchanged for clutch C 9 . Here again the net ratio change is 1.13.  
         [0043]     With both clutches C 8  and C 9  engaged and neither C 4  nor C 5  engaged, output shaft O is locked onto sun gear G 21  and sun gear G 20  of the output planetary gear set. This causes the intermediate carrier and sun gear G 17  to rotate at the same speed, thus forcing intermediate planetary gear set  12  to rotate as a unit. The result is that shaft C and output shaft O rotate at the same speed. Once again, the next two gear selections merely require moving from clutch C 1  to clutch C 2  and then to C 3 , each with a ratio change of 1.13.  
         [0044]     With only a few exceptions,  FIG. 2  shows that the entire sequence of gears is accomplished by selecting one of the 11 available gear ratios in the second section and then stepping through the three forward gear selections in the first section.  
         [0045]     The second section includes a two speed gear section with clutches C 4  and C 5  providing a 1.28 ratio change between their gear sets, an intermediate planetary gear set without a ring gear but with input and output sun gears, and an output simple planetary gear set.  
         [0046]     The two speed gear section includes clutches C 4  and C 5  that provide the choice of two gear sets with different ratios, G 9  to G 10  and G 11  to G 12 . Both of these gear sets are attached to planetary gear carrier CR 1 . Thus, by the selection of either clutch C 4  or clutch C 5 , the speed of carrier CR 1  can be changed relative to the speed of shaft A.  
         [0047]     Inverting planetary gear set  12  provides a ratio inverting function that provides the means for making shifts between any adjacent ratios in the 11 speed second section with a single clutch swap. Shaft C is connected to input sun gear G 14  to provide a reaction member rotating at a reference speed. When C 5  is engaged, G 12  drives G 20  at a lower rotational speed than shaft C, but inverting planetary gear set  12  causes G 21  to rotate at a higher rotational speed than shaft C. As the rotational speed of the inverting carrier is reduced relative to shaft C, the rotational speed of G 17  and G 21  are proportionally increased relative to shaft C. Thus, when G 20  is driving the output shaft, shifting from C 4  to C 5  causes the rotational speed of the output shaft to increase, but when G 21  is driving the output shaft, shifting from C 5  to C 4  causes the rotational speed of the output shaft to increase.  
         [0048]     Output planetary gear set  14  adds still more gear ratios possibilities. One is that clutch C 9  permits carrier CR 2  and output shaft O to be connected directly to output sun gear G 17  of inverting planetary gear set  12  by means of shaft E. Another is that clutch C 8  can connect carrier CR 2  and output shaft O directly to carrier CR 1  of inverting planetary gear set  12 . Furthermore, when both clutches C 8  and C 9  are engaged, output shaft O and both carriers CR 1  and CR 2  are attached to shaft C.  
         [0049]     Moreover, clutches C 6  and C 7  can brake their respective ring gears RG 1  and RG 2  to transmit rotation to carrier CR 2 . When clutch C 6  is engaged carrier CR 2  is driven through the gear reduction of output planetary gear set  14  through its sun gear G 20 , and when clutch C 7  is engaged carrier CR 2  is driven from shaft E through the gear reduction of output planetary gear set  14  through its sun gear G 21 .  
         [0050]     As disclosed in  FIG. 2 , these multiple variations in the gear ratios within the second section of the transmission along with the three forward and one reverse ratio available from the first section of the transmission give the preferred embodiment of the invention the ability to furnish  28  distinct speed variations.  
         [0051]     It is to be understood that the form of this invention as shown is merely a preferred embodiment. Various changes may be made in the function and arrangement of parts; equivalent means may be substituted for those illustrated and described; and certain features may be used independently from others without departing from the spirit and scope of the invention as defined in the following claims.  
         [0052]     For example, bevel gears can also be used within inverting planetary gear set  12 , and different configurations of planetary gear systems, such as the use of a ring gear to replace one sun gear in planetary gear set  12 , can be used to accomplish the same results.