Patent Description:
As a traveling transmission device of a tractor, there is known such device including a speed changer device for speed-changing power of an engine and outputting the speed-changed power, a forward/reverse switchover device provided rearwardly of the speed changer device and configured to switch an output from the speed changer device to a forward traveling power and a reverse traveling power, a rear wheel differential mechanism provided rearwardly of the speed changer device and configured to input the output of the forward/reverse switchover device and transmit it to rear wheels, and a transmission case accommodating the speed changer device, the forward/reverse switchover device and the rear wheel differential mechanism, and configured such that simply with a switchover operation of the forward/reverse switchover device, it is possible to realize forward traveling or reverse traveling at a traveling speed set by the speed changer device. An example of this type of traveling transmission device of a tractor is known from e.g. Patent Document <NUM> (Japanese Unexamined Patent Application Publication <CIT>). In the case of the one disclosed in Patent Document <NUM>, a speed changer transmission device is provided as the speed changer device.

Further, another example of the traveling transmission device of a tractor includes a transmission case to which power from an engine is inputted via an input shaft, a speed changer transmission section provided inside the transmission case and configured to input power from the input shaft and to speed-change the inputted power and to output it, and a rear wheel differential mechanism provided inside the transmission case and configured to input power outputted from the speed changer transmission section and to transmit the inputted power to left and right rear wheels. A further type of this kind of traveling transmission device of a tractor is arranged such that the speed changer transmission section includes a plurality of speed changer sections configured to speed-change and output power from an input shaft via a gear coupling mechanism and a multiple-disc clutch are disposed side by side in a front/rear direction.

An example of this type of traveling transmission device of a tractor known in the art is a speed changer transmission device for a tractor disclosed in Patent Document <NUM>. The speed changer transmission device of a tractor disclosed in Patent Document <NUM> includes a speed changer output section and a forward/reverse switchover device as the speed changer transmission section. The speed changer output section includes an input gear and a speed changer gear as a gear coupling mechanism and includes also a stage divided clutch as a multiple-disc clutch. The forward/reverse switchover device includes a gear coupling mechanism provided between an input shaft and an output shaft and also a forward clutch and a reverse clutch as the multiple-disc clutch.

Since a tractor is to be operably coupled with various kinds of implement such as a fertilizer spraying machine, a rotary cultivator device, a plow, a dozer, etc., there is a need for a tractor capable of driving its wheels at a speed and a torque suitable for a utility work contemplated.

In the traveling transmission device of a tractor having the above-described speed changer transmission section, if the multiple-disc clutch gets into lubricant oil reserved inside the transmission case, the multiple-disc clutch will rotate while receiving rotational resistance due to the lubricant oil, thus increasing power transmission loss. On the other hand, in order to suppress such increase of power transmission loss, if an arrangement is provided to prevent or resist entrance of the multiple-disc clutch into the lubricant oil, this also will prevent or resist entrance of the gear coupling mechanism of the speed changer device into the lubricant oil, thus causing a condition of lubricant oil insufficiency for the gear coupling mechanism.

The present invention provides a traveling transmission device of a tractor that can avoid increase of power transmission loss when the traveling transmission device or the multiple-disc clutch receives rotational resistance from lubricant oil and that yet can supply the lubricant oil sufficiently to the gear coupling mechanism.

A traveling transmission device of a tractor according to the present invention is defined in claim <NUM> and comprises:.

With the above-described arrangement, by changing a gear ratio of the gear transmission mechanism, it is possible e.g. to increase the maximum speed at which the rear wheels can be driven and/or to drive the rear wheels with a high torque. When the front case portion and the rear case portion are separated from each other, it is possible to assemble a gear transmission mechanism selected from a plurality of gear transmission mechanisms having different gear ratios from the front side of the rear case portion with keeping the speed changer device, the forward/reverse switchover device and the rear wheel differential mechanism assembled to each other. Therefore, a tractor capable of driving rear wheels at a speed or torque corresponding to various kinds of utility work can be obtained inexpensively.

In the present invention, preferably:
the traveling transmission device further comprises:.

With the above-described arrangement, since the power from the forward/reverse switchover device is transmitted to the front wheels, not only the rear wheels, but also the front wheels can be driven. Since the second transmission mechanism having a gear ratio corresponding to the gear ratio of the gear transmission mechanism can be assembled from the front side of the rear case portion, like the assembly of the gear transmission mechanism, a tractor capable of driving rear wheels and front wheels at a speed or torque corresponding to various kinds of utility work can be obtained inexpensively.

In the present invention, preferably:
the second gear transmission mechanism is configured to input the power of the output shaft of the rear wheel differential mechanism to the front wheel transmission mechanism.

With the above-described arrangement, since the second gear transmission mechanism takes the forward traveling power or reverse traveling power to be inputted to the front wheel transmission mechanism off the input shaft of the rear wheel differential mechanism, in comparison with an arrangement of taking the power off the forward/reverse switchover device, the forward traveling power or reverse traveling power as the output of the forward/reverse switchover device can be inputted to the front wheel transmission mechanism by a simple arrangement.

In the present invention:
the rear case portion is separable into the front end portion of the rear case portion and the other portion of the rear case portion than the front end portion.

With the above-described arrangement, by removing the front end portion from the other portion than the front end portion, it becomes possible to enlarge the work space for assembly of the gear transmission mechanism, so the gear transmission mechanism can be assembled easily.

With the above-described arrangement, it is possible to allow the rear wheel differential mechanism to get into an amount of lubricant oil reserved inside the transmission case while preventing the composite planetary transmission section from getting into the lubricant oil, so that efficient power transmission is possible with rotation without being subject to resistance due to the lubricant oil.

With the above-described arrangement, even if the stage-divided transmission section does not get into the amount of lubricant oil inside the transmission case like the composite planetary transmission section, oil is still fed to the stage-divided transmission section by the oil feeding section, so that seizure of the stage-divided transmission section can be avoided.

With the above-described arrangement, while the stepless output gear and the planetary input gear are operably coupled with each other via the first relay gear, the relay shaft and the second relay gear, the stepless output gear can be disposed with rearward offset relative to the planetary input gear. Thus, the front/rear length of a stepless case portion accommodating the stepless speed changer section can be made shorter.

With the above-described arrangement, while the PTO gear and the stepless input gear are operably coupled with each other via the third relay gear, the relay shaft and the fourth relay gear, the stepless input gear can be disposed with forward offset relative to the PTO gear. Thus, the front/rear length of a stepless case portion accommodating the stepless speed changer section can be made shorter.

Next, an embodiment as an example of the present invention will be explained with reference to the accompanying drawings.

Incidentally, in the following explanation, with respect to a traveling vehicle body of a tractor, a direction of arrow F shown in <FIG> is defined as "vehicle body front side", a direction of arrow B is defined as "vehicle body rear side", a direction of arrow U is defined as "vehicle body upper side", a direction of arrow D is defined as "vehicle body lower side", a direction on the front (near) side of the plane of drawing is defined as "vehicle body left side" and a direction on the back (far) side of the plane of drawing is defined as "vehicle body right side", respectively.

A traveling vehicle body of a tractor, as shown in <FIG> includes an engine <NUM>, a clutch housing <NUM> coupled to a rear portion of the engine <NUM>, a transmission case <NUM> coupled to a rear portion of the clutch housing <NUM>, and a vehicle body frame <NUM> constituted of a front wheel support frame <NUM> extended from a lower portion of the engine <NUM> to the front side. At front portions of the vehicle body frame <NUM>, a pair of left and right front wheels <NUM> are mounted to be drivable and steerable. At rear portions of the traveling vehicle body frame <NUM>, a pair of left and right rear wheels <NUM> are mounted to be drivable. At a front portion of the traveling vehicle body, there is formed an engine section <NUM>. At rear portions of the traveling vehicle body, there are formed a driver's seat <NUM> and a driving section <NUM> having a steering wheel <NUM> for steering the front wheels <NUM>. In the driving section <NUM>, there is provided a cabin <NUM> which covers the boarding space. At a rear portion of the vehicle body frame <NUM>, there is mounted a link mechanism <NUM> for coupling various kinds of implements such as a rotary cultivator device with allowing elevation and lowering thereof. At a rear portion of the transmission case <NUM>, there is provided a PTO shaft <NUM> for transmitting power from the engine <NUM> to the coupled implement.

A traveling transmission device <NUM> for transmitting power of the engine <NUM> to the front wheels <NUM> and the rear wheels <NUM> is arranged as shown in <FIG>. This traveling transmission device <NUM> includes a speed changer device <NUM> configured to input power of an output shaft 1a of the engine <NUM> from a main clutch <NUM> to an input shaft <NUM>, a forward/reverse switchover device <NUM> configured to input the output of the speed changer device <NUM> and to convert the inputted power to forward traveling power and reverse traveling power, a rear wheel differential mechanism <NUM> configured to input the forward traveling power and the reverse traveling power outputted from the forward/reverse switchover device <NUM> and to transmit the inputted forward traveling power and reverse traveling power to the left and right rear wheels <NUM>, a front wheel transmission mechanism <NUM> configured to input forward traveling power and reverse traveling power outputted from the forward/reverse switchover device <NUM> and to output the inputted forward traveling power and reverse traveling power to the front wheels <NUM>, and a front wheel differential mechanism <NUM> configured to input the forward traveling power and the reverse traveling power outputted from the front wheel transmission mechanism <NUM> and to output the inputted forward traveling power and reverse traveling power to the left and right front wheels <NUM>.

The speed changer device <NUM>, the forward/reverse switchover device <NUM>, the rear wheel differential mechanism <NUM> and the front wheel transmission mechanism <NUM>, as shown in <FIG>, are accommodated in the transmission case <NUM>. The transmission case <NUM>, as shown in <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, is configured to be separable along a first separating line L1 to a front case portion 3A which accommodates the speed changer device <NUM> and the front wheel transmission mechanism <NUM> and a rear case portion 3B which accommodates the forward/reverse switchover device <NUM> and the rear wheel differential mechanism <NUM>. The rear case portion 3B, as shown in <FIG>, <FIG>, <FIG>, <FIG>, is configured to be separable along a second separating line L2 to a front end portion 3C within which a front portion of an output shaft <NUM> of the forward/reverse switchover device <NUM> and a front portion of an input shaft 20a of the rear wheel differential mechanism <NUM> are positioned and a portion 3D in which the portion other than the front end portion is located.

The speed changer device <NUM>, as shown in <FIG>, includes a stepless speed changer section 18A to which the power of the engine <NUM> is inputted, a composite planetary transmission section 18B to which an output of the stepless speed changer section 18A and the power of the engine <NUM> are inputted and a stage-divided transmission section 18C configured to output the output of the composite planetary transmission section 18B in divided stages. <FIG> is a schematic view showing layouts of the composite planetary transmission section 18B, the stepless speed changer section 18A, the rear wheel differential mechanism <NUM>, etc. The direction of arrow U shown in <FIG> indicates "vehicle body upper side" the direction of arrow D indicates "vehicle body lower side", the direction of arrow L indicates "vehicle body left side" and the direction of arrow R indicates "vehicle body right side", respectively. Accommodation of the speed changer device <NUM> into the transmission case <NUM>, as shown in <FIG>, is carried out, as seen in the front/rear direction, such that an output shaft <NUM> of the stage-divided transmission section 18C and an input shaft <NUM> of the forward/reverse switchover device <NUM> are located on one lateral side relative to an axis X of sun gears <NUM>, <NUM> of the composite planetary transmission section 18B and a front/rear oriented axis 37a of a stepless output gear <NUM> of the stepless speed changer section 18A is located on the other lateral side relative to the axis X of the sun gears <NUM>, <NUM> and also the axis X of the sun gears <NUM>, <NUM> is located upwardly of an axis Y of an input shaft 20a of the rear wheel differential mechanism <NUM>.

The stepless speed changer section 18A, as shown in <FIG> and <FIG>, includes a variable displacement and axial plunger type hydraulic pump <NUM>, a fixed displacement and axial plunger type hydraulic motor <NUM> and a driving oil passage <NUM> which connects the hydraulic pump <NUM> with the hydraulic motor <NUM>. The stepless speed changer section 18A is a hydrostatic stepless speed changer section. As shown in <FIG>, a stepless case portion <NUM> of the front case portion 3A which covers the stepless speed changer section 18A is detachable from the other portion of the front case portion 3A than the stepless case portion. As shown in <FIG> and <FIG>, the stepless speed changer section 18A includes a stepless input gear <NUM> rotatably provided at a rear portion of the stepless speed changer section 18A and a stepless output gear <NUM> rotatably provided at a front portion of the stepless speed changer section 18A. The stepless input gear <NUM> is non-rotatably mounted on a pump shaft <NUM> and rotates about a front/rear oriented axis 36a of the pump shaft <NUM>. The stepless output gear <NUM> is non-rotatably mounted on a motor shaft <NUM> and rotates about a front/rear oriented axis 37a of the motor shaft <NUM>.

As shown in <FIG> and <FIG>, between the stepless input gear <NUM> and a portion of a rotational shaft <NUM> inserted in the front/rear direction through an axial portion of the composite planetary transmission section 18B which portion is located rearwardly of the composite planetary transmission section 18B, a second power transmitting mechanism <NUM> is provided. As shown in <FIG>, a front end portion 38a of the rotational shaft <NUM> and a rear end portion 17a of the input shaft <NUM> of the speed changer device <NUM> are non-rotatably engaged with each other via a spline engagement. The second power transmitting mechanism <NUM>, as shown in <FIG> and <FIG>, includes a rotatable second relay shaft <NUM> provided parallel with the front/rear oriented axis 36a of the stepless input gear <NUM>, a PTO gear <NUM> non-rotatably mounted on the rotational shaft <NUM>, a third relay gear <NUM> non-rotatably mounted on a rear end portion of the second relay shaft <NUM> to be meshed with the PTO gear <NUM>, and a fourth relay gear <NUM> non-rotatably mounted on a front end portion of the second relay shaft <NUM> to be meshed with the stepless input gear <NUM>. The second power transmitting mechanism <NUM> transmits the power of the rotational shaft <NUM> to the stepless input gear <NUM>. The rotational shaft <NUM>, as shown in <FIG> is operably coupled with the power takeoff (PTO) shaft <NUM> via a PTO speed changer device <NUM> and transmits the power of the engine <NUM> transmitted to the input shaft <NUM> to the PTO shaft <NUM>.

In the stepless speed changer section 18A, the power of the engine <NUM> which has been transmitted from the output shaft 1a of the engine <NUM> to the rotational shaft <NUM> via the main clutch <NUM> and the input shaft <NUM> is transmitted by the second power transmitting mechanism <NUM> to the stepless input gear <NUM> and speed-changed to power in the forward rotation direction and power in the reverse rotation direction by the hydraulic pump <NUM> and the hydraulic motor <NUM>, the power being speed-changed in stepless manner both in the forward rotation direction and in the reverse rotation direction, and the speed-changed power in the forward rotation direction and speed-changed power in the reverse rotation direction will be outputted from the stepless output gear <NUM>.

As shown in <FIG>, the composite planetary transmission section 18B includes the two sun gears <NUM>,<NUM> and is arranged such that the axis X of the two sun gears <NUM>, <NUM> and an axis Z of the output shaft 1a of the engine <NUM> are located on a single straight line. The composite planetary transmission section 18B includes two rows of planetary gear mechanisms 50A, 50B disposed one after another in the front/rear direction. The planetary gear mechanism 50A in the first row, as shown in <FIG> and <FIG>, includes the sun gear <NUM>, an internal gear <NUM> and three planetary gears <NUM>. The planetary gear mechanism 50B in the second row, as shown in <FIG> and <FIG>, includes the sun gear <NUM>, an internal gear <NUM> and three planetary gears <NUM>. As shown in <FIG>, the planetary gear mechanism 50A in the first row includes three coupling gears <NUM> which are meshed respectively with the three planetary gears <NUM>. As shown in <FIG>, the three coupling gears <NUM> are operably coupled with the three planetary gears <NUM> of the planetary gear mechanism <NUM> in the second row. The operative coupling between the coupling gears <NUM> and the planetary gears <NUM> is realized by forming the coupling gears <NUM> and the planetary gears <NUM> integrally.

As shown in <FIG>, at a front portion of the composite planetary transmission section 18B, there is provided a planetary input gear <NUM> which is non-rotatably and operably coupled with the sun gear <NUM> of the planetary gear mechanism 50A in the first row. The planetary input gear <NUM> is operably coupled to the stepless output gear <NUM> of the stepless speed changer section 18A via the power transmitting mechanism <NUM>. The power transmitting mechanism <NUM>, as shown in <FIG> and <FIG>, includes a rotatable relay shaft <NUM> which is provided parallel with a front/rear oriented axis 37a of the stepless output gear <NUM>, a first relay gear <NUM> which is non-rotatably mounted to a rear portion of the relay shaft <NUM> to be meshed with the stepless output gear <NUM>, and a second relay gear <NUM> which is non-rotatably mounted on a front end portion of the relay shaft <NUM> to be meshed with the planetary input gear <NUM>. Power of the stepless output gear <NUM> is transmitted to the planetary input gear <NUM> via the power transmitting mechanism <NUM> and then inputted to the sun gear <NUM> via the planetary input gear <NUM>.

As shown in <FIG>, at a front portion of the composite planetary transmission section 18B, there is provided a second planetary input gear <NUM> which is non-rotatably and operably coupled with the internal gear <NUM> of the planetary gear mechanism 50A in the first row. The second planetary input gear <NUM> is operably coupled with the input shaft <NUM> via an input transmission mechanism <NUM>. The input transmission mechanism <NUM>, as shown in <FIG>, includes an input shaft gear <NUM> non-rotatably mounted on the input shaft <NUM>, a fourth relay gear <NUM> which is non-rotatably mounted on a front end portion of the third relay shaft <NUM> to be meshed with the input shaft gear <NUM>, and a fifth relay gear <NUM> which is non-rotatably mounted on a rear end portion of the third relay shaft <NUM> to be meshed with the second planetary input gear <NUM>. Power transmitted from the output shaft 1a of the engine <NUM> to the input shaft <NUM> via the main clutch <NUM> is transmitted via the input transmission mechanism <NUM> to the second planetary input gear <NUM> and inputted from this second planetary gear <NUM> to the internal gear <NUM>.

As shown in <FIG>, at a rear portion of the composite planetary transmission section 18B, there are provided a first output shaft <NUM>, a second output shaft <NUM> and a third output shaft <NUM> to be rotatable relative to each other. The first output shaft <NUM>, the second output shaft <NUM> and the third output shaft <NUM> are provided as a triple-shaft arrangement. The first output shaft <NUM> is operably coupled with the internal gear <NUM> of the planetary gear mechanism 50B in the second row. The second output shaft <NUM> is operably coupled with a carrier <NUM>. The carrier <NUM> is configured to support the planetary gear <NUM> of the planetary gear mechanism 50A in the first row and to support also the planetary gear <NUM> of the planetary gear mechanism 50B in the second row. The third output shaft <NUM> is operably coupled with the sun gear <NUM> of the planetary gear mechanism 50B in the second row.

With the composite planetary transmission section 18B in operation, the output in the forward rotation direction and the output in the reverse rotation direction outputted by the stepless speed changer section 18A via the stepless output gear <NUM> is inputted via the power transmitting mechanism <NUM> to the sun gear <NUM> of the planetary gear mechanism 50A in the first row and the power from the engine <NUM> is inputted via the input transmission mechanism <NUM> to the internal gear <NUM> of the planetary gear mechanism 50A in the first row. Then, the output of the stepless speed changer section 18A and the power of the engine <NUM> inputted thereto are synthesized by the planetary gear mechanisms 50A, 50B in the two rows, and the resultant synthesized power is outputted from the first output shaft <NUM>, the second output shaft <NUM> and the third output shaft <NUM>.

The stage-divided transmission section 18C, as shown in <FIG> and <FIG>, includes a first clutch CL1, a second clutch CL2, a third clutch CL3 and a fourth clutch CL4. The first through fourth clutches are constituted as hydraulic operation type multiple-disc clutches. To respective output side rotational members of the first clutch CL1, the second clutch CL2, the third clutch CL3 and the fourth clutch CL4, the output shaft <NUM> is non-rotatably and operably coupled. Between an input side rotational member of the first clutch CL1 and the first output shaft <NUM> of the composite planetary transmission section 18B, there is provided a first speed gear coupling mechanism <NUM> for setting a first speed range. Between an input side rotational member of the second clutch CL2 and the third output shaft <NUM> of the composite planetary transmission section 18B, there is provided a second speed gear coupling mechanism <NUM> for setting a second speed range. Between an input side rotational member of the third clutch CL3 and the second output shaft <NUM> of the composite planetary transmission section 18B, there is provided a third speed gear coupling mechanism <NUM> for setting a third speed range. Between an input side rotational member of the fourth clutch CL4 and the third output shaft <NUM> of the composite planetary transmission section 18B, there is provided a fourth speed gear coupling mechanism <NUM> for setting a fourth speed.

As shown in <FIG>, the first clutch CL1, the second clutch CL2, the third clutch CL3, the fourth clutch CL4 and the stepless speed changer section 18A are coupled to a control device <NUM>. To this control device <NUM>, there are operably coupled an operational position sensor <NUM> for detecting an operational position of the speed changer lever <NUM> and a swash plate sensor <NUM> for detecting a swash plate angle in the hydraulic pump <NUM> of the stepless speed changer section 18A. The control device <NUM> is constituted of a microcomputer and includes a speed changer controlling means <NUM>. The speed changer controlling means <NUM> controls the swash plate of the stepless speed changer section 18A based on a detection result of the operational position sensor <NUM> and a detection result of the swash plate sensor <NUM>, in such a manner that the stepless speed changer section 18A may be rendered into an operational state corresponding to an operational position of the speed changer lever <NUM> and also the stage-divided transmission section 18C may be rendered into an operational stage corresponding to the operational position of the speed changer lever <NUM> and controls also switchovers of the first clutch CL1, the second clutch CL2, the third clutch CL3 and the fourth clutch CL4. The speed changer lever <NUM>, as shown in <FIG>, is configured to be operable to/among a first operational range A1, a second operational range A2, a third operational range A3 and a fourth operational range A4.

<FIG> is an explanatory view showing relation between the operational range of the speed changer lever <NUM> and the operational states of the stage-divided transmission section 18C. In <FIG>, a sign " O" represents engaged states of the first clutch CL1, the second clutch CL2, the third clutch CL3 and the fourth clutch CL4, whereas a sign "-" represents disengaged states of the first clutch CL1, the second clutch CL2, the third clutch CL3 and the fourth clutch CL4. <FIG> is an explanatory view showing relation between speed change states of the stepless speed changer section 18A, speed ranges and output speeds V provided by the output shaft <NUM>. The vertical axis in <FIG> shows the output speed V provided by the output shaft <NUM>, the horizontal axis in <FIG> shows the speed change states of the stepless speed changer section 18A, a sign "N" represents a neutral state, a sign "+MAX" represents a maximum speed state when the output direction is in the forward rotation direction, whereas a sign "-MAX" represents a maximum speed state when the output direction is in the reverse rotation direction.

With the speed changer device <NUM> in operation, as shown in <FIG>, if the speed changer lever <NUM> is operated to the first operational range A1, the first clutch CL1 is controlled to be rendered to the engaged state and as the speed changer lever <NUM> is operated from the lowest speed position to the highest speed position of the first operational range A1, the stepless speed changer section 18A is speed-controlled from the highest speed state in the reverse rotational direction toward the highest speed state in the forward rotational direction, whereby the output speed V of the output shaft <NUM> is increased in the first speed range from zero to V1 in a stepless manner. If the speed changer lever <NUM> is operated to the second operational range A2, the second clutch CL2 is controlled to be rendered to the engaged state and as the speed changer lever <NUM> is operated from the lowest speed state in the forward rotational direction toward the highest speed position in the second operational range A2, the stepless speed changer section 18A is speed-controlled from the highest speed state in the forward rotational direction toward the highest speed state in the reverse rotational direction, whereby the output speed V of the output shaft <NUM> is increased steplessly from V1 to V2 in the second speed range. If the speed changer lever <NUM> is operated to the third operational range A3, the third clutch CL3 is controlled to be rendered to the engaged state and as the speed changer lever <NUM> is operated from the lowest speed position toward the highest speed position in the third operational range A3, the stepless speed changer section 18A is speed-controlled from the highest speed state in the reverse rotational direction toward the highest speed state in the forward rotational direction, whereby the output speed V of the output shaft <NUM> is increased steplessly from V2 to V3 in the third speed range. If the speed changer lever <NUM> is operated to the fourth operational range A4, the fourth clutch CL4 is controlled to be rendered to the engaged state and as the speed changer lever <NUM> is operated from the lowest speed position toward the highest speed position in the fourth operational range A4, the stepless speed changer section 18A is speed-controlled from the highest speed state in the forward rotational direction toward the highest speed state in the reverse rotational direction, whereby the output speed V of the output shaft <NUM> is increased steplessly from V3 to V4 in the fourth speed range.

The forward/reverse switchover device <NUM> and the rear wheel differential mechanism <NUM>, as shown in <FIG>, are provided rearwardly of the speed changer device <NUM>. The forward/reverse switchover device <NUM> includes an input shaft <NUM> which is non-rotatably coupled via a coupling member <NUM> to the output shaft <NUM> (output shaft of the speed changer device <NUM>) of the stage-divided transmission section 18C and an output shaft <NUM> which is disposed parallel with the input shaft <NUM>. The output shaft <NUM> is constituted of a tubular shaft which is non-rotatably fitted on the relay shaft <NUM>. The axis of the output shaft <NUM> is located on the same axis as the axis of the sun gears <NUM>, <NUM> of the composite planetary transmission section 18B. To the input shaft <NUM>, respective input side rotational members of a forward clutch CLF and a reverse clutch CLR are non-rotatably coupled. Between an output side rotational member of the forward clutch CLF and the output shaft <NUM>, there is provided a forward gear mechanism <NUM>. Between an output side rotational member of the reverse clutch CLR and the output shaft <NUM>, there is provided a reverse gear mechanism <NUM>. A reverse rotation gear 93a of the reverse gear mechanism <NUM> is rotatably mounted on the input shaft 20a of the rear wheel differential mechanism <NUM>. Between a front portion of the output shaft <NUM> of the forward/reverse switchover device <NUM> and a front portion of the input shaft 20a of the rear wheel differential mechanism <NUM>, there is provided a gear coupling mechanism <NUM>.

In the forward/reverse switchover device <NUM>, the forward clutch CLF and the reverse clutch CLR are switched over by operations of the forward/reverse lever <NUM> (see <FIG>). When the forward clutch CLF is switched to the engaged state and the reverse clutch CLR is switched to the disengaged state, the power inputted to the input shaft <NUM> from the output shaft <NUM> of the speed changer device <NUM> is converted into forward traveling power by the forward clutch CLF and the forward gear mechanism <NUM> and transmitted as such to the output shaft <NUM>. When the forward clutch CLF is switched to the disengaged state and the reverse clutch CLR is switched to the engaged state, the power inputted to the input shaft <NUM> from the output shaft <NUM> of the speed changer device <NUM> is converted into reverse traveling power by the reverse clutch CLR and the reverse gear mechanism <NUM> and transmitted as such to the output shaft <NUM>.

As shown in <FIG> and <FIG>, the forward traveling power and the reverse traveling power outputted by the forward/reverse switchover device <NUM> via the output shaft <NUM> are transmitted via the gear coupling mechanism <NUM> to the input shaft 20a of the rear wheel differential mechanism <NUM> and then transmitted by the rear wheel differential mechanism <NUM> to the left and right rear wheels <NUM>. As shown in <FIG>, the power transmission from the rear wheel differential mechanism <NUM> to the left and right rear wheels <NUM> is effected via a planetary gear type final reduction mechanism <NUM> provided between the output shaft 20b of the rear wheel differential mechanism <NUM> and a rear axle 7a. On the output shaft 20b of the rear wheel differential mechanism <NUM>, there is provided a steering brake <NUM>.

The front wheel transmission mechanism <NUM>, as shown in <FIG>, includes an input shaft <NUM> operably coupled to a front portion of the input shaft 20a of the rear wheel differential mechanism <NUM> via the second gear coupling mechanism <NUM>, the relay shaft <NUM> and the coupling member <NUM>, and an output shaft <NUM> which is disposed parallel with the input shaft <NUM>. To the input shaft <NUM>, input side rotational members of a constant speed clutch <NUM> and an acceleration clutch <NUM>. Between an output side rotational member of the constant speed clutch <NUM> and the output shaft <NUM>, there is provided a constant speed gear mechanism <NUM> configured to transmit the rotational speed of the input shaft <NUM> at a substantially constant (equal) speed to the output shaft <NUM>. Between an output side rotational member of the acceleration clutch <NUM> and the output shaft <NUM>, there is provided an acceleration gear mechanism <NUM> configured to increase the rotational speed of the input shaft <NUM> and transmit it to the output shaft <NUM>. The output shaft <NUM> is operably coupled with the input shaft 22a of the front wheel differential mechanism <NUM> via the rotational shaft <NUM> and outputs to the left and right front wheels <NUM>.

The second gear coupling mechanism <NUM> is configured such that power of the input shaft 20a to which the power of the output shaft <NUM> is transmitted by the gear coupling mechanism <NUM> is transmitted to the relay shaft <NUM>, whereby the forward traveling power and the reverse traveling power outputted by the forward/reverse switchover device <NUM> via the output shaft <NUM> are transmitted by the second gear coupling mechanism <NUM> to the input shaft <NUM>.

In the front wheel transmission mechanism <NUM>, when the constant speed clutch <NUM> is switched to the engaged state and the acceleration clutch <NUM> is switched to the disengaged state, the power of the input shaft <NUM> which is rotated by power from the forward/reverse switchover device <NUM> transmitted by the second gear coupling mechanism <NUM> and the relay shaft <NUM> is transmitted to the output shaft <NUM> via the constant speed clutch <NUM> and the constant speed gear mechanism <NUM> and outputted from the output shaft <NUM> to the front wheels <NUM>. In this case, there is realized a four wheel drive state in which the front wheels <NUM> and the rear wheels <NUM> are driven with the average circumferential speed of the left and right front wheels <NUM> being substantially equal to the average circumferential speed of the left and right rear wheels <NUM>.

In the front wheel transmission mechanism <NUM>, when the constant speed clutch <NUM> is switched to the disengaged state and the acceleration clutch <NUM> is switched to the engaged state, the power of the input shaft <NUM> which is rotated by power from the forward/reverse switchover device <NUM> transmitted by the second gear coupling mechanism <NUM> and the relay shaft <NUM> is transmitted to the output shaft <NUM> via the acceleration clutch <NUM> and the acceleration gear mechanism <NUM>. In this case, there is realized a front wheel accelerated four wheel drive state in which the front wheels <NUM> and the rear wheels <NUM> are driven with the average circumferential speed of the left and right front wheels <NUM> being higher than the average circumferential speed of the left and right rear wheels <NUM>.

In the front wheel transmission mechanism <NUM>, when both the constant speed clutch <NUM> and the acceleration clutch <NUM> are switched to the disengaged state, power transmission from the input shaft <NUM> to the output shaft <NUM> is stopped, thus stopping output to the front wheels <NUM>. In this case, there is realized a two wheel drive state in which the left and right front wheels <NUM> are not driven, and the left and right rear wheels <NUM> are driven.

The gear coupling mechanism <NUM> which transmits power of the output shaft <NUM> of the forward/reverse switchover device <NUM> to the input shaft 20a of the rear wheel differential mechanism <NUM>, as shown in <FIG>, is detchably provided at a portion of the inside of the transmission case <NUM> which portion corresponds to the front end portion 3C of the rear case portion 3B. More particularly, the gear coupling mechanism <NUM> includes a first gear 95a which is detchably attached to a front end portion of the output shaft <NUM> of the forward/reverse switchover device <NUM> and a second gear 95b which is detchably attached to a front end portion of the input shaft 20a of the rear wheel differential mechanism <NUM> to be meshed with the first gear 95a.

The second gear coupling mechanism <NUM> configured to input power from the forward/reverse switchover device <NUM> to the input shaft <NUM> of the front wheel transmission mechanism <NUM>, as shown in <FIG>, is detachably provided at a portion of the inside of the transmission case <NUM> which portion corresponds to the front end portion 3C of the rear case portion 3B. More particularly, the second gear coupling mechanism <NUM> includes a third gear 100a which is detchably attached to a front end portion of the input shaft 20a of the rear wheel differential mechanism <NUM> and a fourth gear 100b which is detchably attached to the relay shaft <NUM> to be meshed with the third gear 100a. The relay shaft <NUM> is detachably and operably coupled to the input shaft <NUM> of the front wheel transmission mechanism <NUM> via a coupling member <NUM>. To the relay shaft <NUM>, a parking brake 101Ais attached.

When a tractor having a different maximum vehicle speed and/or a different torque transmittable to the front wheels <NUM> and the rear wheels <NUM> is to be obtained. a gear coupling mechanism having a corresponding gear ratio will be selected from a plurality of gear coupling mechanisms <NUM> having different gear ratios from each other and also a second gear coupling mechanism <NUM> having a gear ratio corresponding to the selected gear coupling mechanism <NUM> will be selected from a plurality of second gear coupling mechanisms <NUM> having different gear ratios from each other. Then, the selected gear coupling mechanism <NUM> and the selected second gear coupling mechanism <NUM> will be assembled. This assembling can be done from the front side of the rear case portion 3B which has been separated from the front case portion 3A and from which the front end portion 3C has been separated. For instance, when the traveling transmission device <NUM> is to be newly assembled, after assembling the speed changer device <NUM>, the forward/reverse switchover device <NUM> and the rear wheel differential mechanism <NUM>, the selected gear coupling mechanism <NUM> and second gear coupling mechanism <NUM> can be assembled. At the time of replacement of the gear coupling mechanism <NUM> and the second gear coupling mechanism <NUM>, without having to detach the speed changer device <NUM>, the forward/reverse switchover device <NUM> and the rear wheel differential mechanism <NUM>, the selected gear coupling mechanism <NUM> and the selected second gear coupling mechanism <NUM> can be assembled.

Inside the transmission case <NUM>, as shown in <FIG>, there are provided a first oil feeding section <NUM> for feeding lubricant oil to the stage-divided transmission section 18C and a second oil feeding section <NUM> for feeding lubricant oil to the forward/reverse switchover device <NUM>. In the instant embodiment, the first oil feeding section <NUM> and the second oil feeding section <NUM> are provided. Alternatively, however, it is possible to embody with provision of an oil feeding section for feeding lubricant oil to the composite planetary transmission section 18B.

More particularly, the first oil feeding section <NUM>, as shown in <FIG> and <FIG>, includes an oil feeding pipe <NUM> provided to extend in the front/rear direction above the stage-divided transmission section 18C and discharge nozzles <NUM> formed at portions corresponding respectively to the first speed gear coupling mechanism <NUM>, the second speed gear coupling mechanism <NUM>, the third speed gear coupling mechanism <NUM> and the fourth speed gear coupling mechanism <NUM>. The oil feeding pipe <NUM> is formed integrally with the front case portion 3A. To this oil feeding pipe <NUM>, an oil feeding pump <NUM> is connected.

In the first oil feeding section <NUM>, an amount of lubricant oil reserved in the transmission case <NUM> is taken out by the oil feeding pump <NUM> and fed to the oil feeding pipe <NUM>. And, this fed lubricant oil is discharged from the respective discharge nozzles <NUM> from the upper side toward the corresponding first speed gear coupling mechanism <NUM> or the second speed gear coupling mechanism <NUM> or the third speed gear coupling mechanism <NUM> or the fourth speed gear coupling mechanism <NUM>.

More particularly, the second oil feeding section <NUM>, as shown in <FIG>, includes an oil feeding pipe <NUM> provided to extend in the front/rear direction above the forward/reverse switchover device <NUM> and discharge nozzles <NUM> formed at portions corresponding respectively to the forward gear mechanism <NUM> and the reverse gear mechanism <NUM> of the forward/reverse switchover device <NUM>. The oil feeding pipe <NUM> is formed integrally with the rear case portion 3B. To this oil feeding pipe <NUM>, though not shown, the oil feeding pump <NUM> is connected.

In the second oil feeding section <NUM>, an amount of lubricant oil reserved in the transmission case <NUM> is taken out by the oil feeding pump <NUM> and fed to the oil feeding pipe <NUM>. And, this fed lubricant oil is discharged from the respective discharge nozzles <NUM> from the upper side toward the corresponding forward gear mechanism <NUM> or the reverse gear mechanism <NUM>.

Next, with reference to <FIG>, etc., more detailed explanation will be given on the oil feeding sections <NUM>, <NUM> again.

The traveling transmission device <NUM>, as shown in <FIG>, includes the transmission case <NUM> to which the power from the engine <NUM> is inputted via the input shaft <NUM>. The power transmission from the engine <NUM> to the input shaft <NUM> is done through the operative coupling of the input shaft <NUM> with the output shaft 1a of the engine <NUM> via the main clutch <NUM>. Inside the transmission case <NUM>, there are provided a speed changer transmission section constituted of the stage-divided transmission section 18C, a speed changer transmission section constituted of the forward/reverse switchover device <NUM>, the front wheel transmission mechanism <NUM> which outputs toward the front wheel differential mechanism <NUM> and the rear wheel differential mechanism <NUM> which transmits power to the left and right rear wheels <NUM>.

In the following discussion, the speed changer section constituted of the stage-divided transmission section 18C will be referred to as a first speed changer transmission section 18C and the speed changer transmission section constituted of the forward/reverse switchover device <NUM> will be referred to as a second speed changer transmission section <NUM>, respectively.

The first speed changer transmission section 18C inputs the power from the input shaft <NUM>. More particularly, as shown in <FIG>, the power of the input shaft <NUM> is inputted via the rotational shaft <NUM> and the second power transmitting mechanism <NUM> to the pump shaft <NUM> of the stepless speed changer section 18A. In the stepless speed changer section 18A, the inputted power is speed-changed steplessly by the hydraulic pump <NUM> and the hydraulic motor <NUM> and outputted as such via the motor shaft <NUM>. The output of the stepless speed changer section 18A is inputted via the power transmitting mechanism <NUM> to the sun gear <NUM> of the planetary gear mechanism 50A in the first row of the composite planetary transmission section 18B and the power of the input shaft <NUM> is inputted via the input transmission mechanism <NUM> to the internal gear <NUM> of the planetary gear mechanism 50A in the first row, and in the composite planetary transmission section 18B, the power from the input shaft <NUM> and the power from the stepless speed changer section 18A are synthesized by the planetary gear mechanism 50A in the first row and the planetary gear mechanism 50B in the second row. The resultant synthesized power synthesized by the composite planetary transmission section 18B is inputted to the first speed changer transmission section 18C.

The first speed changer transmission section 18C, as shown in <FIG>, includes four speed changer sections <NUM> juxtaposed in the front/rear direction of the transmission case <NUM> and the output shaft <NUM>. In operation, the synthesized power from the composite planetary transmission section 18B is speed-changed by the four speed changer sections <NUM> and the resultant speed-changed power is outputted from the output shaft <NUM> to the rear wheel differential mechanism <NUM> and the front wheel transmission mechanism <NUM>.

More particularly, as shown in <FIG>, the first speed changer section 23a of the four speed changer sections <NUM> includes the first speed gear coupling mechanism <NUM> of the four gear coupling mechanisms and the first clutch CL1 of the four multiple-disc clutches. The second speed changer section 23b of the four speed changer sections <NUM> includes the second speed gear coupling mechanism <NUM> of the four gear coupling mechanisms and the second clutch CL2 of the four multiple-disc clutches. The third speed changer section 23c of the four speed changer sections <NUM> includes the third speed gear coupling mechanism <NUM> of the four gear coupling mechanisms and the third clutch CL3 of the four multiple-disc clutches. The fourth speed changer section 23d of the four speed changer sections <NUM> includes the fourth speed gear coupling mechanism <NUM> of the four gear coupling mechanisms and the fourth clutch CL4 of the four multiple-disc clutches.

The first through fourth clutches CL1, CL2, CL3 and CL4 are provided on the output shaft <NUM>. The first speed gear coupling mechanism <NUM> is provided between the first output shaft <NUM> of the composite planetary transmission section 18B and an input side member of the first clutch CL1. The second speed gear coupling mechanism <NUM> is provided between the third output shaft <NUM> of the composite planetary transmission section 18B and an input side member of the second clutch CL2. The third speed gear coupling mechanism <NUM> is provided between the second output shaft <NUM> of the composite planetary transmission section 18b and an input side member of the third clutch CL3. The fourth speed gear coupling mechanism <NUM> is provided between the third output shaft <NUM> of the composite planetary transmission section 18B and an input side member of the fourth clutch CL4.

In the first speed changer transmission section 18C, when the first clutch CL1 of only the first speed changer section 23a of the four speed changer sections <NUM> is operated to the engaged stage, the synthesized power outputted by the composite planetary transmission section 18B is speed-changed to driving power in the first speed range (see <FIG>) by the first speed gear coupling mechanism <NUM> and the first clutch CL1 and transmitted as such to the output shaft <NUM> and then transmitted from this output shaft <NUM> to the input shaft <NUM> of the second speed changer transmission section <NUM>. When the second clutch CL2 of only the second speed changer section 23b of the four speed changer sections <NUM> is operated to the engaged stage, the synthesized power outputted by the composite planetary transmission section 18B is speed-changed to driving power in the second speed range (see <FIG>) by the second speed gear coupling mechanism <NUM> and the second clutch CL2 and transmitted as such to the output shaft <NUM> and then transmitted from this output shaft <NUM> to the input shaft <NUM> of the second speed changer transmission section <NUM>. When the third clutch CL3 of only the third speed changer section 23c of the four speed changer sections <NUM> is operated to the engaged stage, the synthesized power outputted by the composite planetary transmission section 18B is speed-changed to driving power in the third speed range (see <FIG>) by the third speed gear coupling mechanism <NUM> and the third clutch CL3 and transmitted as such to the output shaft <NUM> and then transmitted from this output shaft <NUM> to the input shaft <NUM> of the second speed changer transmission section <NUM>. When the fourth clutch CL4 of only the fourth speed changer section 23d of the four speed changer sections <NUM> is operated to the engaged stage, the synthesized power outputted by the composite planetary transmission section 18B is speed-changed to driving power in the fourth speed range (see <FIG>) by the fourth speed gear coupling mechanism <NUM> and the fourth clutch CL4 and transmitted as such to the output shaft <NUM> and then transmitted from this output shaft <NUM> to the input shaft <NUM> of the second speed changer transmission section <NUM>.

The first speed changer transmission section 18C, as shown in <FIG>, is configured such that the output shaft <NUM> is located at a position higher than the input shaft 20a of the rear wheel differential mechanism <NUM>. The first speed changer transmission section 18C, as shown in <FIG>, is configured such that the output shaft <NUM> is located at a position higher than a standard oil surface OS of the lubricant oil reserved in the transmission case <NUM>. The first through fourth clutches CL1, CL2, CL3 and CL4 of the four speed changer sections <NUM> do not get into the lubricant oil significantly, thus being rotatable without receiving much rotational resistance from the lubricant oil.

As shown in <FIG>, inside the transmission case <NUM>, there is provided the oil feeding pipe <NUM> which extends upwardly of the first changer speed transmission section 18C and in the direction of juxtaposition of the four speed changer sections <NUM>. This oil feeding pipe <NUM> has a same arrangement as that of the oil feeding pipe <NUM> provided in the oil feeding section <NUM> shown in <FIG>. The oil feeding pipe <NUM> is formed integrally with the transmission case <NUM>. In the oil feeding pipe <NUM>, at portions thereof corresponding to the respective gear coupling mechanism of the first through fourth speed gear coupling mechanisms <NUM>, <NUM>, <NUM>, <NUM>, discharge nozzles <NUM> are connected for discharging lubricant oil to the respective gear coupling mechanisms <NUM>, <NUM>, <NUM>, <NUM> of the first through fourth speed gear coupling mechanisms <NUM>, <NUM>, <NUM>. The discharge nozzles <NUM> corresponding to the respective gear coupling mechanisms <NUM>, <NUM>, <NUM> of the first speed gear coupling mechanism <NUM>, the third speed gear coupling mechanism <NUM> and the fourth speed gear coupling mechanism <NUM>, as shown in <FIG> and <FIG>, include discharge openings opened downwards toward the respective gear coupling mechanisms <NUM>, <NUM>, <NUM> and discharge the lubricant oil directly toward the gear coupling mechanisms <NUM>, <NUM>, <NUM>. The discharge nozzle <NUM> for discharging the lubricant oil toward the second speed gear coupling mechanism <NUM> of the four gear coupling mechanisms <NUM>, <NUM>, <NUM>, <NUM>, as shown in <FIG> and <FIG>, includes a discharge opening opened rearwards. Rearwardly of the discharge nozzle <NUM> corresponding to the second speed gear coupling mechanism <NUM>, the transmission case <NUM> includes an inclined guide <NUM>. In operation, lubricant oil which hits the inclined guide <NUM> will be guided by this inclined guide <NUM> to flow down toward the second speed gear coupling mechanism <NUM>. The discharge nozzle <NUM> corresponding to the second speed gear coupling mechanism <NUM> discharges the lubricant oil indirectly toward the second speed gear coupling mechanism <NUM>. As shown in <FIG>, the discharge nozzles <NUM> corresponding to the respective gear coupling mechanisms <NUM>, <NUM>, <NUM>, <NUM> of the four gear coupling mechanisms <NUM>, <NUM>, <NUM>, <NUM> have orifices 117a.

As shown in <FIG>, in the wall portion of the transmission case <NUM>, there is defined an oil inlet opening <NUM>. This first oil inlet opening <NUM> is communicated to the oil feeding pipe <NUM> via a communication passage <NUM> (see <FIG>). The oil feeding pump <NUM> is connected to the first oil inlet opening <NUM>, so that when lubricant oil is fed by the oil feeding pump <NUM> to the oil feeding pipe <NUM> via the first oil inlet opening <NUM> and the communication passage <NUM>, the fed lubricant oil is discharged through the discharge nozzles <NUM> toward the respective gear coupling mechanisms of the first through fourth gear coupling mechanisms <NUM>, <NUM>, <NUM> and <NUM>. Irrespectively of changes occurring in the oil pressure in the oil feeding pipe <NUM>, the discharging is effected with the discharge amount being kept constant through the orifices 117a, and the lubricant oil is fed from the upper side to the four speeds gear coupling mechanisms <NUM>, <NUM>, <NUM>, <NUM>. As the output shaft <NUM> is located at the position higher than the standard oil surface OS, not much lubricant oil will enter the first through fourths peed gear coupling mechanisms <NUM>, <NUM>, <NUM>, <NUM>. Yet, with the discharge nozzles <NUM> having the orifices 117a, a constant amount of lubricant oil will be fed to the first through fourth speed gear coupling mechanisms <NUM>, <NUM>, <NUM>, <NUM>.

The second speed changer transmission section <NUM>, as shown in <FIG>, includes the input shaft <NUM> operably coupled via the coupling member <NUM> to the output shaft <NUM> of the first speed changer transmission section 18C and inputs the output of the first speed changer transmission section 18C via the input shaft <NUM>.

The second speed changer transmission section <NUM>, as shown in <FIG>, includes two speed changer sections <NUM> juxtaposed in the front/rear direction of the transmission case <NUM> and the output shaft <NUM> and speed-changes the power transmitted from the first speed changer transmission section 18C to the input shaft <NUM> by the two speed changer sections <NUM> and then outputs the speed-changed power via the output shaft <NUM> to the rear wheel differential mechanism <NUM> and the front wheel transmission mechanism <NUM>.

More particularly, as shown in <FIG>, the forward traveling speed changer section 25a as one of the two speed changer sections <NUM>, includes the forward gear mechanism <NUM> and the forward clutch CLF. The reverse traveling speed changer section 25b, as the other one of the two speed changer sections <NUM>, includes the reverse gear mechanism <NUM> and the reverse clutch CLR. The forward clutch CLF and the reverse clutch CLR are constituted of multiple-disc clutches and provided on the input shaft <NUM>. The forward gear mechanism <NUM> is provided between the output side member of the forward clutch CLF and the output shaft <NUM>. The reverse gear mechanism <NUM> is provided between the output side member of the reverse clutch CLR and the output shaft <NUM>.

In the second speed changer transmission section <NUM>, when the forward clutch CLF is engaged, the power of the input shaft <NUM> transmitted form the first speed changer transmission section 18C is speed-changed into forward traveling power via the forward clutch CLF and the forward gear mechanism <NUM> and the forward traveling power of the output shaft <NUM> is transmitted via the gear coupling mechanism <NUM> to the input shaft 20a of the rear wheel differential mechanism <NUM>. Further, the forward traveling power of the output shaft <NUM> is transmitted via the gear coupling mechanism <NUM>, the input shaft 20a and the second gear coupling mechanism <NUM> to the input shaft <NUM> of the front wheel transmission mechanism <NUM>. When the reverse clutch CLR is operated to the engaged state, the power of the input shaft <NUM> is speed-changed by the reverse clutch CLR and the reverse gear mechanism <NUM> into reverse traveling power and outputted as such to the output shaft <NUM> and the reverse traveling power of the output shaft <NUM> is transmitted via the gear coupling mechanism <NUM> to the input shaft 20a of the rear wheel differential mechanism <NUM>. Further, the reverse traveling power of the output shaft <NUM> is transmitted via the gear coupling mechanism <NUM>, the input shaft 20a and the second gear coupling mechanism <NUM> to the input shaft <NUM> of the front wheel transmission mechanism <NUM>.

The second speed changer transmission section <NUM>, as shown in <FIG>, is configured such that the input shaft <NUM> and the output shaft <NUM> are located at positions higher than the input shaft 20a of the rear wheel differential mechanism <NUM> and also that the output shaft <NUM> is located at a position higher than the standard oil surface OS of the lubricant oil reserved in the transmission case <NUM>. Thus, the forward clutch CLF and the reverse clutch CLR do not get into the lubricant oil significantly, thus rotating without receiving much rotational resistance due to the lubricant oil.

As shown in <FIG>, inside the transmission case <NUM>, there is provided the oil feeding pipe <NUM> which extends upwardly of the second speed changer transmission section <NUM> and in the direction of juxtaposition of the two speed changer sections <NUM>. This oil feeding pipe <NUM> has a same arrangement as the oil feeding pipe <NUM> included in the oil feeding section <NUM> shown in <FIG>. The oil feeding pipe <NUM> is formed integrally with the transmission case <NUM>. In the oil feeding pipe <NUM>, at portions thereof corresponding to the respective gear mechanisms <NUM>, <NUM> of the forward gear mechanism <NUM> and the respective gear mechanism <NUM>, there are connected discharge nozzles <NUM> for discharging lubricant oil toward the respective gear mechanisms <NUM>, <NUM>. The discharge nozzle <NUM> corresponding to the forward gear mechanism <NUM>, as shown in <FIG> and <FIG>, has a discharge opening which is opened downwards toward the forward gear mechanism <NUM> and discharges lubricant oil directly toward the forward gear mechanism <NUM>. The discharge nozzle <NUM> corresponding to the reverse gear mechanism <NUM>, as shown in <FIG> and <FIG>, has a discharge opening which is opened forwardly. Forwardly of the discharge nozzle <NUM> corresponding to the reverse gear mechanism <NUM>, the transmission case <NUM> includes an inclined guide <NUM>. In operation, lubricant oil which hits the inclined guide <NUM> will be guided by this inclined guide <NUM> to flow down toward the reverse gear mechanism <NUM>. The discharge nozzle <NUM> corresponding to the reverse gear mechanism <NUM> discharges the lubricant oil indirectly toward the reverse gear mechanism <NUM>. As shown in <FIG>, the discharge nozzles <NUM> corresponding to the respective gear mechanisms <NUM>, <NUM> of the forward gear mechanism <NUM> and the reverse gear mechanism <NUM> have orifices 122a.

As shown in <FIG>, in the wall portion of the transmission case <NUM>, there is defined a second oil inlet opening <NUM>. This second oil inlet opening <NUM> is communicated to the oil feeding pipe <NUM> via a communication passage <NUM> (see <FIG>). The oil feeding pump <NUM> is connected to the second oil inlet opening <NUM>, so that when lubricant oil is fed by the oil feeding pump <NUM> to the oil feeding pipe <NUM> via the second oil inlet opening <NUM> and the communication passage <NUM>, the fed lubricant oil is discharged through the discharge nozzles <NUM> toward the forward gear mechanism <NUM> and the reverse gear mechanism <NUM>. Irrespectively of changes occurring in the oil pressure in the oil feeding pipe <NUM>, the discharging is effected with the discharge amount being kept constant through the orifices 122a, and the lubricant oil is fed at constant amount from the upper side to the forward gear mechanism <NUM> and the reverse gear mechanism <NUM>. Although the forward gear mechanism <NUM> and the reverse gear mechanism <NUM> do not get into the lubricant oil significantly, a constant amount of lubricant oil is fed by the oil feeding pipe <NUM> and the discharge nozzles <NUM> having the orifices 122a.

Claim 1:
A traveling transmission device of a tractor comprising:
a speed changer device (<NUM>) for speed-changing power from an engine (<NUM>) and output it, the speed changer device including a stepless speed changer section (18A) to which a power of the engine is inputted, a composite planetary transmission section (18B) to which an output of the stepless speed changer section and the power of the engine are inputted, and a stage-divided transmission section (18C) configured to output the output of the composite planetary transmission section in divided stages;
a forward/reverse switchover device (<NUM>) configured to switch the output of the speed changer device into/between a forward traveling power and a reverse traveling power;
a rear wheel differential mechanism (<NUM>) provided rearwardly of the speed changer device and configured to input the output of the forward/reverse switchover device and transmit it to rear wheels (<NUM>);
a gear transmission mechanism (<NUM>) configured to transmit power of an output shaft of the forward/reverse switchover device to an input shaft (20a) of the rear wheel differential mechanism; and
a transmission case (<NUM>) accommodating the speed changer device, the forward/reverse switchover device, the rear wheel differential mechanism and the gear transmission mechanism;
wherein the transmission case includes a front case portion (3A) which accommodates the speed changer device and a rear case portion (3B) which accommodates the forward/reverse switchover device, the rear wheel differential mechanism and the gear transmission mechanism, with the front case portion and the rear case portion being separable from each other;
characterized in that:
the gear transmission mechanism is detachably attached to a portion of inside of the transmission case which portion corresponds to a front end portion (3C) of the rear case portion; and
the rear case portion (3B) is separable into the front end portion (3C) of the rear case portion and another portion of the rear case portion (3D) than the front end portion (3C).