Transmission

1. A transmission for a tractor, the transmission comprising:

a hydraulic unit configured to operate with a working fluid; and

a transmission housing which accommodates or supports the hydraulic unit, the transmission housing comprising:

a main block that defines:

a chamber to accommodate the hydraulic unit; and

an oil hole configured to guide the working fluid to the hydraulic unit,

a center block attached to the main block, and

a front cover attached to the center block;

a seal case directly attached to the center block and provided with a support part for a shaft configured to transmit rotary power, the seal case defining a plurality of oil grooves configured to guide the working fluid to the hydraulic unit; and

an elongated pipe having a first end coupled to the seal case and configured to introduce the working fluid to the seal case; and

wherein:

the transmission housing defines a flow path of the working fluid from the main block through the oil hole, to the seal case via the elongated pipe, through a first oil groove of the plurality of oil grooves, and to the shaft, and

during operation of the transmission, the plurality of oil grooves of the seal case guide the working fluid to an advancing/backing-switching device, a front-wheel drive switching device, and a work-machine drive switching device.

2. The transmission for the tractor according to claim 1 , wherein:

the hydraulic unit comprises:

the advancing/backing-switching device,

the front-wheel drive switching device, and

the work-machine drive switching device.

3. The transmission for the tractor according to claim 1 , wherein:

the seal case is directly coupled to the center block; and

the center block is directly coupled to the front cover.

4. A transmission comprising:

a hydraulic unit which operates with a working fluid;

a housing which accommodates or supports the hydraulic unit, the housing comprising:

a main block that defines one or more first holes;

a center block coupled to the main block, the center block having a first side and a second side; and

a front cover directly coupled to the second side of the center block;

a seal case defining one or more grooves and configured to receive a first shaft configured to transmit rotary power, the seal case directly coupled to the first side of the center block, and positioned between the main block and the center block with reference to an axial direction of the first shaft; and

a first elongated pipe aligned in the axial direction and coupled to the seal case and configured to guide the working fluid;

wherein:

the housing defines a passage for guiding the working fluid to the hydraulic unit;

the seal case is attached to the housing, and a first groove of the one or more grooves forms a first portion of the passage for guiding the working fluid to the hydraulic unit; and

the seal case is coupled to the first elongated pipe via a connection part.

5. The transmission according to claim 4 , wherein:

the hydraulic unit comprises a front-wheel drive switching device that includes a second shaft; and

the passage defines a first flow path of the working fluid from the main block, through the first elongated pipe, to the seal case, through the first groove of the one or more grooves, and to the first second shaft.

6. The transmission according to claim 5 , wherein:

the hydraulic unit comprises an advancing/backing switching device;

the center block defines one or more second holes; and

the passage defines a second flow path of the working fluid from the main block, through the one or more first holes, through the one or more second holes, to the advancing/backing switching device.

7. The transmission according to claim 4 , wherein:

the hydraulic unit comprises a work-machine drive switching device;

the one or more grooves of the seal case cooperate with the center block to define one or more passages; and

the first elongated pipe extends from the seal case to the main block and is distinct from the center block.

8. The transmission according to claim 7 , wherein:

a second groove of the one or more grooves of the seal case forms a second portion of the passage for guiding the working fluid to the work-machine drive switching device; and

the passage defines a third flow path of the working fluid from the main block through the one or more first holes, to the center block, to the seal case, through the second groove, through the center block, to the work-machine drive switching device.

9. The transmission according to claim 4 , wherein the housing further comprises a rear cover, the rear cover and the front cover positioned on opposing sides of the main block.

10. The transmission according to claim 4 , further comprising:

a hydraulic pump configured to pressure-feed the working fluid to the hydraulic unit,

wherein the housing has an oil chamber formed on an attachment seating surface of the hydraulic pump, the oil chamber being configured to be closed by the hydraulic pump.

11. The transmission according to claim 10 , wherein:

the housing defines the passage for guiding the working fluid between one or more clutches of the hydraulic unit to the oil chamber.

12. A transmission comprising:

a hydraulic unit configured to operate with a working fluid, the hydraulic unit comprising at least one of:

an advancing/backing-switching device,

a front-wheel drive switching device, or

a work-machine drive switching device;

a housing enclosing at least a portion of the hydraulic unit and configured to guide the working fluid to the hydraulic unit, the housing comprising:

a main block comprising a first surface that defines a first set of one or more holes;

a center block directly coupled to the main block and to a front cover such that the center block is interposed between the main block and the front cover; and

a seal case configured to receive a shaft configured to transmit rotary power, directly coupled to the center block, and interposed between the main block and the center block with reference to an axial direction of the shaft, the seal case directly coupled to the center block and defining:

one or more oil grooves configured to guide the working fluid to the hydraulic unit; and

a second set of one or more holes; and

one or more elongated pipes aligned in the axial direction and configured to deliver the working fluid to the seal case.

13. The transmission according to claim 12 , wherein:

the housing further comprises:

the front cover directly coupled to the center block; and

one or more electromagnetic valves; and

the center block defines a third set of one or more holes.

14. The transmission according to claim 13 , wherein:

the housing defines a first flow path from a first electromagnetic valve of the one or more electromagnetic valves, through a first and second hole of the first set of one or more holes of the main block, to the center block, through a first and second hole of the third set of one or more holes of the center block, to a first clutch.

15. The transmission according to claim 14 , wherein the housing defines a second flow path from the first electromagnetic valve, through a third and fourth hole of the first set of one or more holes of the main block, through a first pipe of the one or more elongated pipes, to a first groove of the one or more oil grooves of the seal case, through a first hole of the second set of one or more holes of the seal case, to a second clutch.

16. The transmission according to claim 14 , wherein:

the housing defines a third flow path from the first electromagnetic valve, through a fifth and sixth hole of the first set of one or more holes of the main block, to a first groove defined by the center block, through a third hole of the third set of one or more holes of the center block, to a third groove of the one or more oil grooves of the seal case through a second hole of the second set of one or more holes of the seal case, to a second groove defined by the center block, through a fourth hole of the third set of one or more holes of the center block, to the front cover, through a first hole defined by the front cover, through a second electromagnetic valve of the one or more electromagnetic valves, to a third clutch.

17. The transmission according to claim 16 , wherein the front cover defines an oil chamber.

18. The transmission according to claim 17 , wherein the hydraulic unit comprises:

the advancing/backing switching device;

the front-wheel drive switching device;

the work-machine drive switching device; and

the main block defines a chamber configured to receive a portion of the hydraulic unit.

19. The transmission according to claim 13 , wherein:

the front cover is coupled to a first side of the center block;

the main block and the seal case are coupled to a second side of the center block opposite the first side; and

the seal case is directly coupled to the center block.