Patent Description:
<CIT> discloses a transmission falling within the wording of the pre-characterizing portion of claim <NUM>.

Further disclosed in Patent Literature <NUM> and Patent Literature <NUM> is a transmission designed for use in a tractor or other work machine such as an agricultural machine or a construction machine. The transmission includes a first shaft, a second shaft, and a third shaft. Disposed on the first shaft are three gears connected and disconnected by three clutches and one gear coupling to the first shaft. Disposed on the second shaft are three gears connected and disconnected by two clutches and one gear coupling to the second shaft. Disposed on the third shaft are three gears coupling to the third shaft. The gears disposed on the individual shafts constantly mesh with each other, and gear ratios are selected by switching the clutches.

However, according to the technologies disclosed in Patent Literature <NUM> and Patent Literature <NUM>, three clutches are disposed on the first shaft while no clutch is disposed on the third shaft. Therefore, the first shaft is increased in length. This causes a problem where the transmission requires an increased space.

The present invention has been made to solve the above problems, and has an object to provide a transmission capable of achieving space saving.

The above object is achieved by a transmission according to claim <NUM>.

According to the transmission defined in claim <NUM>, power of the first shaft is transmitted to the second shaft in order from the first gear to the third gear, and simultaneously transmitted to the third shaft in order from the first gear to the sixth gear. When the first clutch is engaged, the power of the first shaft is transmitted to the fourth shaft in order from the second gear to the ninth gear. Power of the second shaft is transmitted to the fourth shaft in order from the fourth gear to the ninth gear when the second clutch is engaged. Power of the third shaft is transmitted to the fourth shaft in order from the seventh gear to the ninth gear when the fourth clutch is engaged. Disposing clutches on the first to third shafts makes it possible to prevent each shaft from becoming excessively long. This results in space saving.

According to the transmission defined in claim <NUM>, the power of the second shaft is transmitted to the fourth shaft in order from a fifth gear to a tenth gear when a third clutch is engaged. The power of the third shaft is transmitted to the fourth shaft in order from an eighth gear to the tenth gear when a fifth clutch is engaged. This increases the number of paths of power transmission to the fourth shaft. Consequently, in addition to the advantageous effect provided by claim <NUM>, it is possible to further increase the number of transmission speeds.

In addition, also according to the transmission defined in claim <NUM>, a fifth shaft parallel to the fourth shaft is additionally included. Power of the fourth shaft is transmitted to the fifth shaft in order from a twelfth gear to a fourteenth gear when a sixth clutch is engaged, and transmitted to the fifth shaft in order from an eleventh gear to an eighteenth gear when an eighth clutch is engaged. This increases the number of paths of power transmission from the fourth shaft to the fifth shaft.

Consequently, it is possible to further increase the number of transmission speeds.

According to the transmission defined in claim <NUM>, second shaft and the third shaft drive respective hydraulic pumps. Consequently, in addition to the advantageous effect provided by claim <NUM> or <NUM>, it is possible to drive many hydraulic pumps.

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. <FIG> is a skeleton diagram illustrating a transmission <NUM> according to an embodiment of the present invention. The transmission <NUM> is mounted in a tractor or other work machine (not depicted) such as an agricultural machine or a construction machine.

The transmission <NUM> includes a first shaft <NUM>, a second shaft <NUM>, a third shaft <NUM>, a fourth shaft <NUM>, a fifth shaft <NUM>, and a sixth shaft <NUM>. These shafts are disposed in parallel to each other. The first shaft <NUM> acts as an input shaft. The second shaft <NUM>, the third shaft <NUM>, the fourth shaft <NUM>, and the fifth shaft <NUM> act as intermediate shafts. The sixth shaft <NUM> acts as an output shaft. Power of a driving source <NUM>, such as an engine or a torque converter, is inputted to the first shaft <NUM>. A PTO (Power take-off) <NUM> is disposed on the first shaft <NUM>. Hydraulic pumps <NUM>, <NUM> are respectively disposed on both ends of the second and third shafts <NUM>, <NUM>. The hydraulic pumps <NUM>, <NUM> are hydraulic power sources for a hydraulic system (not depicted), for example, of clutches for connecting and disconnecting the individual shafts or a rotary or lifter of a work machine. The transmission <NUM> outputs power from a front output member <NUM> and a rear output member <NUM>. The front output member <NUM> and the rear output member <NUM> are disposed on the sixth shaft <NUM>.

A first gear <NUM> couples to the first shaft <NUM>. The first shaft <NUM> rotatably supports a second gear <NUM> by using a bearing (not depicted). The second gear <NUM> couples to the first shaft <NUM> when a first clutch <NUM> is engaged, and idles around the first shaft <NUM> when the first clutch <NUM> is disengaged.

A third gear <NUM> couples to the second shaft <NUM>. The second shaft <NUM> rotatably supports a fourth gear <NUM> and a fifth gear <NUM> by using bearings (not depicted). The third gear <NUM> meshes with the first gear <NUM>. The fourth gear <NUM> couples to the second shaft <NUM> when a second clutch <NUM> is engaged, and idles around the second shaft <NUM> when the second clutch <NUM> is disengaged. The fifth gear <NUM> couples to the second shaft <NUM> when a third clutch <NUM> is engaged, and idles around the second shaft <NUM> when the third clutch <NUM> is disengaged.

A sixth gear <NUM> couples to the third shaft <NUM>. The third shaft <NUM> rotatably supports a seventh gear <NUM> and a eighth gear <NUM> by using bearings (not depicted). The sixth gear <NUM> meshes with the first gear <NUM>. The seventh gear <NUM> couples to the third shaft <NUM> when a fourth clutch <NUM> is engaged, and idles around the third shaft <NUM> when the fourth clutch <NUM> is disengaged. The eighth gear <NUM> couples to the third shaft <NUM> when a fifth clutch <NUM> is engaged, and idles around the third shaft <NUM> when the fifth clutch <NUM> is disengaged.

A ninth gear <NUM>, a tenth gear <NUM>, and an eleventh gear <NUM> couple to the fourth shaft <NUM>. The fourth shaft <NUM> rotatably supports a twelfth gear <NUM> and a thirteenth gear <NUM> by using bearings (not depicted). The ninth gear <NUM> meshes with the second gear <NUM>, the fourth gear <NUM>, and the seventh gear <NUM>. The tenth gear <NUM> meshes with the fifth gear <NUM> and the eighth gear <NUM>. The twelfth gear <NUM> couples to the fourth shaft <NUM> when a sixth clutch <NUM> is engaged, and idles around the fourth shaft <NUM> when the sixth clutch <NUM> is disengaged. The thirteenth gear <NUM> couples to the fourth shaft <NUM> when a seventh clutch <NUM> is engaged, and idles around the fourth shaft <NUM> when the seventh clutch <NUM> is disengaged.

A fourteenth gear <NUM>, a fifteenth gear <NUM>, a sixteenth gear <NUM>, and a seventeenth gear <NUM> couple to the fifth shaft <NUM>. The fifth shaft <NUM> rotatably supports an eighteenth gear <NUM> and a nineteenth gear <NUM> by using bearings (not depicted). The fourteenth gear <NUM> meshes with the twelfth gear <NUM>. The fifteenth gear <NUM> meshes with the thirteenth gear <NUM>. The eighteenth gear <NUM> meshes with the eleventh gear <NUM>. The nineteenth gear <NUM> meshes with the tenth gear <NUM>. The eighteenth gear <NUM> couples to the fifth shaft <NUM> when an eighth clutch <NUM> is engaged, and idles around the fifth shaft <NUM> when the eighth clutch <NUM> is disengaged. The nineteenth gear <NUM> couples to the fifth shaft <NUM> when a ninth clutch <NUM> is engaged, and idles around the fifth shaft <NUM> when the ninth clutch <NUM> is disengaged.

The sixth shaft <NUM> rotatably supports a twentieth gear <NUM> and a twenty-first gear <NUM> by using bearings (not depicted). The twentieth gear <NUM> meshes with the sixteenth gear <NUM>. The twenty-first gear <NUM> meshes with the seventeenth gear <NUM>. The twentieth gear <NUM> couples to the sixth shaft <NUM> when a tenth clutch <NUM> is engaged, and idles around the sixth shaft <NUM> when the tenth clutch <NUM> is disengaged. The twenty-first gear <NUM> couples to the sixth shaft <NUM> when an eleventh clutch <NUM> is engaged, and idles around the sixth shaft <NUM> when the eleventh clutch <NUM> is disengaged. In the present embodiment, the first clutch <NUM> to eleventh clutch <NUM> are hydraulic friction clutches.

<FIG> is a schematic front view of the transmission <NUM>. <FIG> is a cross-sectional view of the transmission <NUM> taken along line III-III in <FIG>. <FIG> is a cross-sectional view of the transmission taken along line IV-IV in <FIG> does not depict the teeth of each gear. <FIG> and <FIG> do not depict the interior of each of the clutches <NUM>, <NUM>, <NUM>, <NUM> and <NUM>.

As depicted in <FIG>, the third gear <NUM> on the second shaft <NUM> and the sixth gear <NUM> on the third shaft <NUM> mesh with the first gear <NUM> on the first shaft <NUM> so that the power of the first shaft <NUM> is transmitted to the second shaft <NUM> and the third shaft <NUM>. As power is transmitted to the fourth shaft <NUM> through the second gear <NUM> on the first shaft <NUM>, the fourth gear <NUM> on the second shaft <NUM>, and the seventh gear <NUM> on the third shaft <NUM>, it is possible to suppress dimensions in the direction perpendicular to the first shaft <NUM> to the fourth shaft <NUM>.

As depicted in <FIG> and <FIG>, the second gear <NUM> on the first shaft <NUM> and the seventh gear <NUM> on the third shaft <NUM> mesh with the ninth gear <NUM> on the fourth shaft <NUM>. Therefore, the number of gears disposed on the fourth shaft <NUM> can be made smaller than in a case where gears in mesh with the second gear <NUM> and gears in mesh with the seventh gear <NUM> are both disposed on the fourth shaft <NUM>. Further, as no more than two clutches are disposed on each shaft, it is possible to suppress dimensions in the direction perpendicular to and dimensions in the axial direction of the first shaft <NUM> to the fourth shaft <NUM>. This makes it possible to save the space required for the transmission <NUM>. As a result, the transmission <NUM> can easily be mounted in a work machine (not depicted).

Further description will now be given with reference again to <FIG>. The transmission <NUM> is configured such that the clutches are disposed on all the shafts from the first shaft <NUM> to the sixth shaft <NUM>. One clutch is disposed on the first shaft <NUM>, and two clutches are disposed on each of the second shaft <NUM> to the sixth shaft <NUM>. As no more than two clutches are disposed on each shaft, it is possible to suppress the lengths of the shafts on which the clutches are disposed.

<FIG> is a chart illustrating clutch engagement combinations of the transmission <NUM>. The transmission <NUM> is able to have thirty-two forward gear positions (F1 to F32) and eight reverse gear positions (R1 to R8) by shifting gears to switch the first clutch <NUM> to the eleventh clutch <NUM> (marked <NUM> to <NUM> in <FIG>). The clutches to be engaged at each gear position are marked × in <FIG>. Three clutches are simultaneously engaged at each gear position. The transmission <NUM> is able to select a predetermined gear ratio by performing an operation for switching the first clutch <NUM> to the eleventh clutch <NUM>.

When shifting into neutral, the transmission <NUM> disengages the first clutch <NUM>, the second clutch <NUM>, the third clutch <NUM>, the fourth clutch <NUM>, and the fifth clutch <NUM>. As a result, no power is transmitted to shafts other than the first shaft <NUM>, the second shaft <NUM>, and the third shaft <NUM>. The third gear <NUM> coupling to the second shaft <NUM> and the sixth gear <NUM> coupling to the third shaft <NUM> mesh with the first gear <NUM> coupling to the first shaft <NUM>. Therefore, when the first shaft <NUM> rotates, the second shaft <NUM> and the third shaft <NUM> always rotate. Consequently, the hydraulic pumps <NUM>, <NUM> connected to both ends of the second and third shafts <NUM>, <NUM> always operate when the first shaft <NUM> rotates.

When shifting into the first forward gear position (F1), the transmission <NUM> engages the second clutch <NUM>, the sixth clutch <NUM>, and the tenth clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the third gear <NUM>, the fourth gear <NUM>, the ninth gear <NUM>, the twelfth gear <NUM>, the fourteenth gear <NUM>, the sixteenth gear <NUM>, and the twentieth gear <NUM>.

When shifting into the second forward gear position (F2), the transmission <NUM> engages the third clutch <NUM>, the sixth clutch <NUM>, and the tenth clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the third gear <NUM>, the fifth gear <NUM>, the tenth gear <NUM>, the twelfth gear <NUM>, the fourteenth gear <NUM>, the sixteenth gear <NUM>, and the twentieth gear <NUM>.

When shifting into the third forward gear position (F3), the transmission <NUM> engages the fourth clutch <NUM>, the sixth clutch <NUM>, and the tenth clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the sixth gear <NUM>, the seventh gear <NUM>, the ninth gear <NUM>, the twelfth gear <NUM>, the fourteenth gear <NUM>, the sixteenth gear <NUM>, and the twentieth gear <NUM>.

When shifting into the fourth forward gear position (F4), the transmission <NUM> engages the fifth clutch <NUM>, the sixth clutch <NUM>, and the tenth clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the sixth gear <NUM>, the eighth gear <NUM>, the tenth gear <NUM>, the twelfth gear <NUM>, the fourteenth gear <NUM>, the sixteenth gear <NUM>, and the twentieth gear <NUM>.

When shifting into the fifth forward gear position (F5), the transmission <NUM> engages the second clutch <NUM>, the eighth clutch <NUM>, and the tenth clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the third gear <NUM>, the fourth gear <NUM>, the ninth gear <NUM>, the eleventh gear <NUM>, the eighteenth gear <NUM>, the sixteenth gear <NUM>, and the twentieth gear <NUM>.

When shifting into the sixth forward gear position (F6), the transmission <NUM> engages the third clutch <NUM>, the eighth clutch <NUM>, and the tenth clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the third gear <NUM>, the fifth gear <NUM>, the tenth gear <NUM>, the eleventh gear <NUM>, the eighteenth gear <NUM>, the sixteenth gear <NUM>, and the twentieth gear <NUM>.

When shifting into the seventh forward gear position (F7), the transmission <NUM> engages the fourth clutch <NUM>, the eighth clutch <NUM>, and the tenth clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the sixth gear <NUM>, the seventh gear <NUM>, the ninth gear <NUM>, the eleventh gear <NUM>, the eighteenth gear <NUM>, the sixteenth gear <NUM>, and the twentieth gear <NUM>.

When shifting into the eighth forward gear position (F8), the transmission <NUM> engages the fifth clutch <NUM>, the eighth clutch <NUM>, and the tenth clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the sixth gear <NUM>, the eighth gear <NUM>, the tenth gear <NUM>, the eleventh gear <NUM>, the eighteenth gear <NUM>, the sixteenth gear <NUM>, and the twentieth gear <NUM>.

When shifting into the ninth forward gear position (F9), the transmission <NUM> engages the second clutch <NUM>, the ninth clutch <NUM>, and the tenth clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the third gear <NUM>, the fourth gear <NUM>, the ninth gear <NUM>, the tenth gear <NUM>, the nineteenth gear <NUM>, the sixteenth gear <NUM>, and the twentieth gear <NUM>.

When shifting into the tenth forward gear position (F10), the transmission <NUM> engages the third clutch <NUM>, the ninth clutch <NUM>, and the tenth clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through seven gears in the order of the first gear <NUM>, the third gear <NUM>, the fifth gear <NUM>, the tenth gear <NUM>, the nineteenth gear <NUM>, the sixteenth gear <NUM>, and the twentieth gear <NUM>.

When shifting into the eleventh forward gear position (F11), the transmission <NUM> engages the fourth clutch <NUM>, the ninth clutch <NUM>, and the tenth clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the sixth gear <NUM>, the seventh gear <NUM>, the ninth gear <NUM>, the tenth gear <NUM>, the nineteenth gear <NUM>, the sixteenth gear <NUM>, and the twentieth gear <NUM>.

When shifting into the twelfth forward gear position (F12), the transmission <NUM> engages the fifth clutch <NUM>, the ninth clutch <NUM>, and the tenth clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through seven gears in the order of the first gear <NUM>, the sixth gear <NUM>, the eighth gear <NUM>, the tenth gear <NUM>, the nineteenth gear <NUM>, the sixteenth gear <NUM>, and the twentieth gear <NUM>.

When shifting into the thirteen forward gear position (F13), the transmission <NUM> engages the second clutch <NUM>, the seventh clutch <NUM>, and the tenth clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the third gear <NUM>, the fourth gear <NUM>, the ninth gear <NUM>, the thirteenth gear <NUM>, the fifteenth gear <NUM>, the sixteenth gear <NUM>, and the twentieth gear <NUM>.

When shifting into the fourteen forward gear position (F14), the transmission <NUM> engages the third clutch <NUM>, the seventh clutch <NUM>, and the tenth clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the third gear <NUM>, the fifth gear <NUM>, the tenth gear <NUM>, the thirteenth gear <NUM>, the fifteenth gear <NUM>, the sixteenth gear <NUM>, and the twentieth gear <NUM>.

When shifting into the fifteen forward gear position (F15), the transmission <NUM> engages the fourth clutch <NUM>, the seventh clutch <NUM>, and the tenth clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the sixth gear <NUM>, the seventh gear <NUM>, the ninth gear <NUM>, the thirteenth gear <NUM>, the fifteenth gear <NUM>, the sixteenth gear <NUM>, and the twentieth gear <NUM>.

When shifting into the sixteenth forward gear position (F16), the transmission <NUM> engages the fifth clutch <NUM>, the seventh clutch <NUM>, and the tenth clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the sixth gear <NUM>, the eighth gear <NUM>, the tenth gear <NUM>, the thirteenth gear <NUM>, the fifteenth gear <NUM>, the sixteenth gear <NUM>, and the twentieth gear <NUM>.

When shifting into the seventeenth forward gear position (F17), the transmission <NUM> engages the second clutch <NUM>, the sixth clutch <NUM>, and the eleventh clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the third gear <NUM>, the fourth gear <NUM>, the ninth gear <NUM>, the twelfth gear <NUM>, the fourteenth gear <NUM>, the seventeenth gear <NUM>, and the twenty-first gear <NUM>.

When shifting into the eighteenth forward gear position (F18), the transmission <NUM> engages the third clutch <NUM>, the sixth clutch <NUM>, and the eleventh clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the third gear <NUM>, the fifth gear <NUM>, the tenth gear <NUM>, the twelfth gear <NUM>, the fourteenth gear <NUM>, the seventeenth gear <NUM>, and the twenty-first gear <NUM>.

When shifting into the nineteenth forward gear position (F19), the transmission <NUM> engages the fourth clutch <NUM>, the sixth clutch <NUM>, and the eleventh clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the sixth gear <NUM>, the seventh gear <NUM>, the ninth gear <NUM>, the twelfth gear <NUM>, the fourteenth gear <NUM>, the seventeenth gear <NUM>, and the twenty-first gear <NUM>.

When shifting into the twentieth forward gear position (F20), the transmission <NUM> engages the fifth clutch <NUM>, the sixth clutch <NUM>, and the eleventh clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the sixth gear <NUM>, the eighth gear <NUM>, the tenth gear <NUM>, the twelfth gear <NUM>, the fourteenth gear <NUM>, the seventeenth gear <NUM>, and the twenty-first gear <NUM>.

When shifting into the twenty-first forward gear position (F21), the transmission <NUM> engages the second clutch <NUM>, the eighth clutch <NUM>, and the eleventh clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the third gear <NUM>, the fourth gear <NUM>, the ninth gear <NUM>, the eleventh gear <NUM>, the eighteenth gear <NUM>, the seventeenth gear <NUM>, and the twenty-first gear <NUM>.

When shifting into the twenty-second forward gear position (F22), the transmission <NUM> engages the third clutch <NUM>, the eighth clutch <NUM>, and the eleventh clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the third gear <NUM>, the fifth gear <NUM>, the tenth gear <NUM>, the eleventh gear <NUM>, the eighteenth gear <NUM>, the seventeenth gear <NUM>, and the twenty-first gear <NUM>.

When shifting into the twenty-third forward gear position (F23), the transmission <NUM> engages the fourth clutch <NUM>, the eighth clutch <NUM>, and the eleventh clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the sixth gear <NUM>, the seventh gear <NUM>, the ninth gear <NUM>, the eleventh gear <NUM>, the eighteenth gear <NUM>, the seventeenth gear <NUM>, and the twenty-first gear <NUM>.

When shifting into the twenty-fourth forward gear position (F24), the transmission <NUM> engages the fifth clutch <NUM>, the eighth clutch <NUM>, and the eleventh clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the sixth gear <NUM>, the eighth gear <NUM>, the tenth gear <NUM>, the eleventh gear <NUM>, the eighteenth gear <NUM>, the seventeenth gear <NUM>, and the twenty-first gear <NUM>.

When shifting into the twenty-fifth forward gear position (F25), the transmission <NUM> engages the second clutch <NUM>, the ninth clutch <NUM>, and the eleventh clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the third gear <NUM>, the fourth gear <NUM>, the ninth gear <NUM>, the tenth gear <NUM>, the nineteenth gear <NUM>, the seventeenth gear <NUM>, and the twenty-first gear <NUM>.

When shifting into the twenty-sixth forward gear position (F26), the transmission <NUM> engages the third clutch <NUM>, the ninth clutch <NUM>, and the eleventh clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through seven gears in the order of the first gear <NUM>, the third gear <NUM>, the fifth gear <NUM>, the tenth gear <NUM>, the nineteenth gear <NUM>, the seventeenth gear <NUM>, and the twenty-first gear <NUM>.

When shifting into the twenty-seventh forward gear position (F27), the transmission <NUM> engages the fourth clutch <NUM>, the ninth clutch <NUM>, and the eleventh clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the sixth gear <NUM>, the seventh gear <NUM>, the ninth gear <NUM>, the tenth gear <NUM>, the nineteenth gear <NUM>, the seventeenth gear <NUM>, and the twenty-first gear <NUM>.

When shifting into the twenty-eighth forward gear position (F28), the transmission <NUM> engages the fifth clutch <NUM>, the ninth clutch <NUM>, and the eleventh clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through seven gears in the order of the first gear <NUM>, the sixth gear <NUM>, the eighth gear <NUM>, the tenth gear <NUM>, the nineteenth gear <NUM>, the seventeenth gear <NUM>, and the twenty-first gear <NUM>.

When shifting into the twenty-ninth forward gear position (F29), the transmission <NUM> engages the second clutch <NUM>, the seventh clutch <NUM>, and the eleventh clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the third gear <NUM>, the fourth gear <NUM>, the ninth gear <NUM>, the thirteenth gear <NUM>, the fifteenth gear <NUM>, the seventeenth gear <NUM> and the twenty-first gear <NUM>.

When shifting into the thirtieth forward gear position (F30), the transmission <NUM> engages the third clutch <NUM>, the seventh clutch <NUM>, and the eleventh clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the third gear <NUM>, the fifth gear <NUM>, the tenth gear <NUM>, the thirteenth gear <NUM>, the fifteenth gear <NUM>, the seventeenth gear <NUM> and the twenty-first gear <NUM>.

When shifting into the thirty-first forward gear position (F31), the transmission <NUM> engages the fourth clutch <NUM>, the seventh clutch <NUM>, and the eleventh clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the sixth gear <NUM>, the seventh gear <NUM>, the ninth gear <NUM>, the thirteenth gear <NUM>, the fifteenth gear <NUM>, the seventeenth gear <NUM> and the twenty-first gear <NUM>.

When shifting into the thirty-second forward gear position (F32), the transmission <NUM> engages the fifth clutch <NUM>, the seventh clutch <NUM>, and the eleventh clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through eight gears in the order of the first gear <NUM>, the sixth gear <NUM>, the eighth gear <NUM>, the tenth gear <NUM>, the thirteenth gear <NUM>, the fifteenth gear <NUM>, the seventeenth gear <NUM> and the twenty-first gear <NUM>.

When shifting into the first reverse gear position (R1), the transmission <NUM> engages the first clutch <NUM>, the sixth clutch <NUM>, and the tenth clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through six gears in the order of the second gear <NUM>, the ninth gear <NUM>, the twelfth gear <NUM>, the fourteenth gear <NUM>, the sixteenth gear <NUM>, and the twentieth gear <NUM>.

When shifting into the second reverse gear position (R2), the transmission <NUM> engages the first clutch <NUM>, the eighth clutch <NUM>, and the tenth clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through six gears in the order of the second gear <NUM>, the ninth gear <NUM>, the eleventh gear <NUM>, the eighteenth gear <NUM>, the sixteenth gear <NUM>, and the twentieth gear <NUM>.

When shifting into the third reverse gear position (R3), the transmission <NUM> engages the first clutch <NUM>, the ninth clutch <NUM>, and the tenth clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through six gears in the order of the second gear <NUM>, the ninth gear <NUM>, the tenth gear <NUM>, the nineteenth gear <NUM>, the sixteenth gear <NUM>, and the twentieth gear <NUM>.

When shifting into the fourth reverse gear position (R4), the transmission <NUM> engages the first clutch <NUM>, the seventh clutch <NUM>, and the tenth clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through six gears in the order of the second gear <NUM>, the ninth gear <NUM>, the thirteenth gear <NUM>, the fifteenth gear <NUM>, the sixteenth gear <NUM>, and the twentieth gear <NUM>.

When shifting into the fifth reverse gear position (R5), the transmission <NUM> engages the first clutch <NUM>, the sixth clutch <NUM>, and the eleventh clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through six gears in the order of the second gear <NUM>, the ninth gear <NUM>, the twelfth gear <NUM>, the fourteenth gear <NUM>, the seventeenth gear <NUM>, and the twenty-first gear <NUM>.

When shifting into the sixth reverse gear position (R6), the transmission <NUM> engages the first clutch <NUM>, the eighth clutch <NUM>, and the eleventh clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through six gears in the order of the second gear <NUM>, the ninth gear <NUM>, the eleventh gear <NUM>, the eighteenth gear <NUM>, the seventeenth gear <NUM>, and the twenty-first gear <NUM>.

When shifting into the seventh reverse gear position (R7), the transmission <NUM> engages the first clutch <NUM>, the ninth clutch <NUM>, and the eleventh clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through six gears in the order of the second gear <NUM>, the ninth gear <NUM>, the tenth gear <NUM>, the nineteenth gear <NUM>, the seventeenth gear <NUM>, and the twenty-first gear <NUM>.

When shifting into the eighth reverse gear position (R8), the transmission <NUM> engages the first clutch <NUM>, the seventh clutch <NUM>, and the eleventh clutch <NUM>, and disengages the other clutches. The power of the first shaft <NUM> is transmitted to the sixth shaft <NUM> through six gears in the order of the second gear <NUM>, the ninth gear <NUM>, the thirteenth gear <NUM>, the fifteenth gear <NUM>, the seventeenth gear <NUM>, and the twenty-first gear <NUM>.

At an agricultural land or other work place, the transmission <NUM> mainly uses low to intermediate gear positions under normal conditions. When moving a vehicle to a work place, the transmission <NUM> mainly uses a high gear position. As the transmission <NUM> is able to obtain many different gear positions, an optimum gear ratio can be selected both for moving a vehicle and for performing work. The transmission <NUM> transmits the torque of the first shaft <NUM> to the sixth shaft <NUM> through a maximum of only eight gears. This makes it possible to reduce the loss caused by gear meshing.

At any gear position, the transmission <NUM> applies torque to the twentieth gear <NUM> or twenty-first gear <NUM> on the sixth shaft <NUM>. Therefore, as compared with a case where torque is applied to a plurality of gears on the sixth shaft <NUM>, it is possible to reduce the load on a bearing (not depicted) supporting a gear on the sixth shaft <NUM>, which provides high torque. Consequently, as compared with the case where torque is applied to the plurality of gears on the sixth shaft <NUM>, it is possible to prolong the life of the bearing supporting a gear on the sixth shaft <NUM>.

As the hydraulic pumps <NUM>, <NUM> are respectively connected to both ends of the second and third shafts <NUM>, <NUM>, it is possible to drive the many hydraulic pumps <NUM>, <NUM> (four hydraulic pumps in the present embodiment). It should be noted that the number of hydraulic pumps <NUM>, <NUM> to be connected to the second and third shafts <NUM>, <NUM> can be set within a range of one to four hydraulic pumps.

The present invention has been described in terms of an embodiment. However, the present invention is not limited to the above-described embodiment. It will be easily understood by those skilled in the art that various improvements and modifications may be made without departing from the transmission as defined in the claims.

The foregoing embodiment has been described with reference to the thirty-two forward gear positions and eight reverse gear positions of the transmission <NUM>. However, such gear positions are merely illustrative, and the present invention is not limited to such gear positions. Obviously, in consideration of step ratio and operability, some of such gear positions may be omitted from the transmission <NUM> (e.g., the forward gear positions F17 to F19 may be omitted from <FIG> to provide twenty-nine forward gear positions and eight reverse gear positions).

The foregoing embodiment has been described with reference to a case where power is outputted from the front output member <NUM> and rear output member <NUM> disposed on the sixth shaft <NUM>. However, the present invention is not limited to such a configuration. Obviously, the sixth shaft <NUM> may be omitted so as to dispose the front output member <NUM> and the rear output member <NUM> on the fifth shaft <NUM>. Further, it is obvious that the fifth shaft <NUM> and the sixth shaft <NUM> may be omitted so as to dispose the front output member <NUM> and the rear output member <NUM> on the fourth shaft <NUM>.

Claim 1:
A transmission(<NUM>) at least comprising:
a first shaft(<NUM>);
a second shaft(<NUM>);
a third shaft(<NUM>); and
a fourth shaft(<NUM>);
wherein the first, second, third, and fourth shafts(<NUM>,<NUM>,<NUM>,<NUM>) are parallel to each other;
wherein the first shaft(<NUM>) includes a first gear(<NUM>) and a second gear(<NUM>), the first gear(<NUM>) coupling to the first shaft(<NUM>), the second gear(<NUM>) coupling to or idling around the first shaft(<NUM>) when a first clutch(<NUM>) is switched;
wherein the second shaft(<NUM>) includes a third gear(<NUM>) and a fourth gear(<NUM>), the third gear(<NUM>) meshing with the first gear(<NUM>) and coupling to the second shaft(<NUM>), the fourth gear(<NUM>) coupling to or idling around the second shaft(<NUM>) when a second clutch(<NUM>) is switched;
wherein the third shaft(<NUM>) includes a sixth gear(<NUM>) and a seventh gear(<NUM>), the sixth gear(<NUM>) meshing with the first gear(<NUM>) and coupling to the third shaft(<NUM>), the seventh gear(<NUM>) coupling to or idling around the third shaft(<NUM>) when a fourth clutch(<NUM>) is switched; and
wherein the fourth shaft(<NUM>) includes a ninth gear(<NUM>), the ninth gear(<NUM>) meshing with the second gear(<NUM>), the fourth gear(<NUM>), and the seventh gear(<NUM>), and coupling to the fourth shaft(<NUM>), characterized in that
the transmission(<NUM>) further comprises:
a fifth shaft(<NUM>) that is parallel to the fourth shaft(<NUM>);
wherein the fourth shaft(<NUM>) includes an eleventh gear(<NUM>) and a twelfth gear(<NUM>), the eleventh gear(<NUM>) coupling to the fourth shaft(<NUM>), the twelfth gear(<NUM>) coupling to or idling around the fourth shaft(<NUM>) when a sixth clutch(<NUM>) is switched; and
wherein the fifth shaft(<NUM>) includes a fourteenth gear(<NUM>) and an eighteenth gear(<NUM>), the fourteenth gear(<NUM>) meshing with the twelfth gear(<NUM>) and coupling to the fifth shaft(<NUM>), the eighteenth gear(<NUM>) meshing with the eleventh gear(<NUM>), and coupling to or idling around the fifth shaft(<NUM>) when an eighth clutch(<NUM>) is switched.