1. A work vehicle transmission comprising: a plurality of transmission shafts that extend parallel with each other in a front-rear direction of a vehicle body, the plurality of transmission shafts including a speed change shaft and a deceleration shaft; and a multi-stage transmission apparatus including: a first transmission mechanism configured to change input motive power to any one of a plurality of speeds, the first transmission mechanism having a plurality of speed change gear sets, and a plurality of speed change multi-disc clutches that are arranged adjacent in the front-rear direction on the speed change shaft and engage and disengage power transmission to the plurality of speed change gear sets; and a second transmission mechanism configured to change motive power changed by the first transmission mechanism to any one of a plurality of speeds, the number of speeds of the second transmission mechanism being smaller than the number of speeds of the first transmission mechanism, and the second transmission mechanism having a plurality of deceleration gear sets, and a plurality of deceleration multi-disc clutches that are arranged on the deceleration shaft and engage and disengage power transmission to the plurality of deceleration gear sets, wherein the plurality of speed change multi-disc clutches are arranged parallel with the plurality of deceleration multi-disc clutches so as to be adjacent in a diameter direction thereof.

2. The work vehicle transmission according to claim 1, wherein the plurality of transmission shafts includes an intermediate shaft arranged between the speed change shaft and the deceleration shaft.

3. The work vehicle transmission according to claim 2, wherein the speed change shaft, the deceleration shaft and the intermediate shaft are arranged forming an isosceles triangle having the intermediate shaft as an upper vertex in a front view of the vehicle body.

4. The work vehicle transmission according to any one of claims 1 to 3, wherein diameter-direction sizes of the plurality of speed change multi-disc clutches and the plurality of deceleration multi-disc clutches are set to the same size.

5. A work vehicle comprising the work vehicle transmission according to any one of claims 1 to 4.

6. A work vehicle transmission comprising: a plurality of transmission shafts that extend parallel with each other in a front-rear direction of a vehicle body, the plurality of transmission shafts including a speed change shaft and a deceleration shaft; and a multi-stage transmission apparatus including: a first transmission mechanism configured to change input motive power to any one of a plurality of speeds, the first transmission mechanism having a plurality of speed change gear sets, and a plurality of speed change multi-disc clutches that are arranged adjacent in the front-rear direction on the speed change shaft and engage and disengage power transmission to the plurality of speed change gear sets; and a second transmission mechanism configured to change motive power changed by the first transmission mechanism to any one of a plurality of speeds, the number of speeds of the second transmission mechanism being smaller than the number of speeds of the first transmission mechanism, and the second transmission mechanism having a plurality of deceleration gear sets, and a plurality of deceleration multi-disc clutches that are arranged on the deceleration shaft and engage and disengage power transmission to the plurality of deceleration gear sets, wherein the plurality of transmission shafts further includes an intermediate shaft arranged between the speed change shaft and deceleration shaft, the speed change multi-disc clutches and the deceleration multi-disc clutches not being arranged coaxially with the intermediate shaft, and in a front view of the vehicle body, assuming that there are formed a pair of triangular virtual spaces that each has, as one side, a virtual line interconnecting an axis of the speed change shaft and an axis of the deceleration shaft and that are above and below the virtual line, the intermediate shaft is inserted into one of the virtual spaces.

7. The work vehicle transmission according to claim 6, wherein the plurality of speed change multi-disc clutches and the plurality of deceleration multi-disc clutches are arranged so as to be adjacent in a right-left direction of the vehicle body, and in a front view of the vehicle body, the pair of virtual spaces are respectively formed above and below a position between the speed change multi-disc clutches and the deceleration multi-disc clutches.

8. The work vehicle transmission according to claim 7, further comprising: a drive switching apparatus that includes a multi-disc clutch and is configured to switch a transmission state with respect to right and left front wheels by an engaging/disengaging operation of the multi-disc clutch, wherein the drive switching apparatus is arranged below the transmission apparatus in a state where an upper portion of the multi-disc clutch is inserted into the virtual space on a lower side in the front view of the vehicle body.

9. The work vehicle transmission according to any one of claims 6 to 8, wherein diameter-direction sizes of the plurality of speed change multi-disc clutches and the plurality of deceleration multi-disc clutches are set to the same size.

10. A work vehicle comprising the work vehicle transmission according to any one of claims 6 to 9.

11. A work vehicle transmission comprising: a transmission case that also serves as an oil tank; a plurality of hydraulic devices arranged inside the transmission case; and a valve unit configured to control a flow of oil to the hydraulic devices, wherein the transmission case includes a valve unit attachment portion to which the valve unit is to be attached from outside the transmission case, the valve unit has a base plate to be attached to the valve unit attachment portion, and a valve block having a plurality of electromagnetic valves, and the valve unit attachment portion is provided with a recessed portion that defines and forms a storage compartment for the valve block along with the base plate.

12. The work vehicle transmission according to claim 11, wherein the valve unit attachment portion includes an oil return passage configured to return excess oil from the valve block into the transmission case at a position higher, with respect to a vertical direction of the vehicle body, than the valve block in the recessed portion.

13. The work vehicle transmission according to claim 12, wherein a plurality of the oil return passages are formed in two sections vertically in the valve unit attachment portion.

14. The work vehicle transmission according to claim 13, wherein the oil return passages are formed such that an opening area of the oil return passage in an upper section is smaller than an opening area of the oil return passage in a lower section.

15. The work vehicle transmission according to any one of claims 12 to 14, wherein the recessed portion has a lower recession portion in which the valve block is stored, and an upper recession portion that is in communication with an interior of the transmission case via the oil return passage, and the upper recession portion is formed with a shallower recession depth than the lower recession portion and a smaller area than the lower recession portion.

16. The work vehicle transmission according to any one of claims 12 to 15, wherein an oil filter is provided in the oil return passage.

17. The work vehicle transmission according to any one of claims 11 to 16, wherein the plurality of electromagnetic valves includes a plurality of electromagnetic on/off valves and a plurality of electromagnetic proportional valves, the valve block includes a first valve block that has the plurality of electromagnetic on/off valves, and a second valve block that has the plurality of electromagnetic proportional valves, the first valve block is attached to a storage compartment forming surface of the base plate that forms the storage compartment along with the recessed portion, and the second valve block is attached to an outer surface of the base plate on a side opposite to the storage compartment forming surface.

18. The work vehicle transmission according to any one of claims 11 to 17, wherein a partition wall is formed as a single piece with the transmission case, the partition wall supporting the plurality of transmission shafts provided in the transmission case, the plurality of hydraulic devices includes a plurality of transmission switching apparatuses arranged on the plurality of transmission shafts, the valve unit attachment portion is formed at a predetermined position in a front-rear direction of the vehicle body at which the partition wall is formed in the transmission case, and the partition wall is provided with a plurality of inner oil passages that extend between a plurality of connection ports formed in the valve unit and a plurality of oil passages formed in the plurality of transmission shafts.

19. A work vehicle comprising the work vehicle transmission according to any one of claims 11 to 18.

WE CLAIM:
1. A work vehicle transmission comprising:
a plurality of transmission shafts that extend parallel with each other in a front-rear direction of a vehicle body, the plurality of transmission shafts including a speed change shaft and a deceleration shaft; and
a multi-stage transmission apparatus including:
a first transmission mechanism configured to change input motive power to any one of a plurality of speeds, the first transmission mechanism having a plurality of speed change gear sets, and a plurality of speed change multi-disc clutches that are arranged adjacent in the front-rear direction on the speed change shaft and engage and disengage power transmission to the plurality of speed change gear sets; and
a second transmission mechanism configured to change motive power changed by the first transmission mechanism to any one of a plurality of speeds, the number of speeds of the second transmission mechanism being smaller than the number of speeds of the first transmission mechanism, and the second transmission mechanism having a plurality of deceleration gear sets, and a plurality of deceleration multi-disc clutches that are arranged on the deceleration shaft and engage and disengage power transmission to the plurality of deceleration gear sets,
wherein the plurality of speed change multi-disc clutches are arranged parallel with the plurality of deceleration multi-disc clutches so as to be adjacent in a diameter direction thereof.
2. The work vehicle transmission according to claim 1, wherein
the plurality of transmission shafts includes an intermediate shaft arranged between the speed change shaft and the deceleration shaft.
3. The work vehicle transmission according to claim 2, wherein
the speed change shaft, the deceleration shaft and the intermediate shaft are arranged forming an isosceles triangle having the intermediate shaft as an upper vertex in a front view of the vehicle body.
4. The work vehicle transmission according to any one of claims 1 to 3,
wherein
diameter-direction sizes of the plurality of speed change multi-disc clutches

and the plurality of deceleration multi-disc clutches are set to the same size.
5. A work vehicle comprising the work vehicle transmission according to any one of claims 1 to 4.
6. A work vehicle transmission comprising:
a plurality of transmission shafts that extend parallel with each other in a front-rear direction of a vehicle body, the plurality of transmission shafts including a speed change shaft and a deceleration shaft; and
a multi-stage transmission apparatus including:
a first transmission mechanism configured to change input motive power to any one of a plurality of speeds, the first transmission mechanism having a plurality of speed change gear sets, and a plurality of speed change multi-disc clutches that are arranged adjacent in the front-rear direction on the speed change shaft and engage and disengage power transmission to the plurality of speed change gear sets; and
a second transmission mechanism configured to change motive power changed by the first transmission mechanism to any one of a plurality of speeds, the number of speeds of the second transmission mechanism being smaller than the number of speeds of the first transmission mechanism, and the second transmission mechanism having a plurality of deceleration gear sets, and a plurality of deceleration multi-disc clutches that are arranged on the deceleration shaft and engage and disengage power transmission to the plurality of deceleration gear sets,
wherein the plurality of transmission shafts further includes an intermediate shaft arranged between the speed change shaft and deceleration shaft, the speed change multi-disc clutches and the deceleration multi-disc clutches not being arranged coaxially with the intermediate shaft, and
in a front view of the vehicle body, assuming that there are formed a pair of triangular virtual spaces that each has, as one side, a virtual line interconnecting an axis of the speed change shaft and an axis of the deceleration shaft and that are above and below the virtual line, the intermediate shaft is inserted into one of the virtual spaces.
7. The work vehicle transmission according to claim 6, wherein
the plurality of speed change multi-disc clutches and the plurality of deceleration multi-disc clutches are arranged so as to be adjacent in a right-left

direction of the vehicle body, and
in a front view of the vehicle body, the pair of virtual spaces are respectively formed above and below a position between the speed change multi-disc clutches and the deceleration multi-disc clutches.
8. The work vehicle transmission according to claim 7, further comprising:
a drive switching apparatus that includes a multi-disc clutch and is configured to switch a transmission state with respect to right and left front wheels by an engaging/disengaging operation of the multi-disc clutch,
wherein the drive switching apparatus is arranged below the transmission apparatus in a state where an upper portion of the multi-disc clutch is inserted into the virtual space on a lower side in the front view of the vehicle body.
9. The work vehicle transmission according to any one of claims 6 to 8,
wherein
diameter-direction sizes of the plurality of speed change multi-disc clutches and the plurality of deceleration multi-disc clutches are set to the same size.
10. A work vehicle comprising the work vehicle transmission according to any one of claims 6 to 9.
11. A work vehicle transmission comprising:
a transmission case that also serves as an oil tank;
a plurality of hydraulic devices arranged inside the transmission case; and a valve unit configured to control a flow of oil to the hydraulic devices, wherein the transmission case includes a valve unit attachment portion to
which the valve unit is to be attached from outside the transmission case,
the valve unit has a base plate to be attached to the valve unit attachment
portion, and a valve block having a plurality of electromagnetic valves, and
the valve unit attachment portion is provided with a recessed portion that
defines and forms a storage compartment for the valve block along with the base
plate.
12. The work vehicle transmission according to claim 11, wherein
the valve unit attachment portion includes an oil return passage configured to return excess oil from the valve block into the transmission case at a position

higher, with respect to a vertical direction of the vehicle body, than the valve block in the recessed portion.
13. The work vehicle transmission according to claim 12, wherein
a plurality of the oil return passages are formed in two sections vertically in the valve unit attachment portion.
14. The work vehicle transmission according to claim 13, wherein
the oil return passages are formed such that an opening area of the oil return passage in an upper section is smaller than an opening area of the oil return passage in a lower section.
15. The work vehicle transmission according to any one of claims 12 to 14,
wherein
the recessed portion has a lower recession portion in which the valve block is stored, and an upper recession portion that is in communication with an interior of the transmission case via the oil return passage, and
the upper recession portion is formed with a shallower recession depth than the lower recession portion and a smaller area than the lower recession portion.
16. The work vehicle transmission according to any one of claims 12 to 15,
wherein
an oil filter is provided in the oil return passage.
17. The work vehicle transmission according to any one of claims 11 to 16,
wherein
the plurality of electromagnetic valves includes a plurality of electromagnetic on/off valves and a plurality of electromagnetic proportional valves,
the valve block includes a first valve block that has the plurality of electromagnetic on/off valves, and a second valve block that has the plurality of electromagnetic proportional valves,
the first valve block is attached to a storage compartment forming surface of the base plate that forms the storage compartment along with the recessed portion, and
the second valve block is attached to an outer surface of the base plate on a

side opposite to the storage compartment forming surface.
18. The work vehicle transmission according to any one of claims 11 to 17,
wherein
a partition wall is formed as a single piece with the transmission case, the partition wall supporting the plurality of transmission shafts provided in the transmission case,
the plurality of hydraulic devices includes a plurality of transmission switching apparatuses arranged on the plurality of transmission shafts,
the valve unit attachment portion is formed at a predetermined position in a front-rear direction of the vehicle body at which the partition wall is formed in the transmission case, and
the partition wall is provided with a plurality of inner oil passages that extend between a plurality of connection ports formed in the valve unit and a plurality of oil passages formed in the plurality of transmission shafts.
19. A work vehicle comprising the work vehicle transmission according to any
one of claims 11 to 18.