Tractor

The present invention provides a tractor 1 constructed so that an engine 2 is mounted on the front portion of a traveling vehicle body having front wheels 19 and rear wheels 11, a transmission case 3 is provided at the rear portion of the traveling vehicle body, an output shaft 2a of the engine 2 and a transmission input shaft 5 provided on the front face of the transmission case 3 are joined to each other by a first universal joint 6, and a work machine 24 is attached between the front and rear wheels 19 and 11 in a manner enabling it to rise and fall, wherein a front wheel traveling input shaft 15 is provided sat the rear portion of the front axle housing 14 that supports the front wheels 19 so as to project rearward to the inclined upper side, and this front wheel traveling input shaft 15 and a front wheel driving shaft 13 projecting from the transmission case 3 are joined to each other by a second universal joint 17. A first universal joint 6 is provided at the horizontal center of the traveling vehicle body in a planar view, the second universal joint 17 is provided so as to deflect horizontally, and the first universal joint 6 is provided higher than the second universal joint 17 when they are viewed from the side, whereby a work machine 24 mounted to the lower portion of the traveling vehicle body can be lifted high from the ground.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a tractor for mowing or earthing-up by attaching various work machines to the lower portion of a traveling vehicle body having front wheels and rear wheels.

2. Description of the Related Art

Tractors for mowing by attaching a work machine such as a mower to the lower portion of a traveling vehicle body have been generally known. For example, the tractor disclosed in Japanese Unexamined Patent Publication No. H09-272350 is constructed so that a mower is attached to the lower body portion between the front wheels and rear wheels, the driving force of the engine side is transmitted by a universal joint to the transmission case side, a mid PTO shaft projecting from the front face of the transmission case and an input shaft at the mower side are joined by other universal joints to drive mowing blades, and a front wheel driving shaft that also projects from the front face of the transmission case and a front wheel traveling input shaft provided at the rear portion of the front axle housing are joined by a universal joint so that the front wheels are also driven.

Generally, when a tractor travels across farm fields or roads after finishing mowing, a work machine such as a mower must be lifted high from the ground so as not to obstruct traveling. In the case of the abovementioned conventional tractor, to prevent the driving force transmission shaft for driving front wheels from obstructing lifting of the mower, the driving force transmission shaft is located close to the machine frame and extended forward parallel to the ground, the front end of the driving force transmission shaft is supported on the machine frame side by a special bearing, a transmission case for raising the position of the input shaft is provided at the front axle housing side, and the input shaft of this transmission case side and the front end of the driving force transmission shaft are joined to each other via a separate middle shaft, whereby the front wheels are driven.

Therefore, in this prior art, the structure for driving the front wheels is complicated and a bearing and a transmission case are required, resulting in an increase in the number of parts and manufacturing costs.

SUMMARY OF THE INVENTION

An object of the invention is to provide a tractor which can be constructed at low cost without installation of a special bearing and an extra transmission case, and can lift a work machine such as a mower to a height above the ground.

Another object of the invention is to improve operability of a work machine that is connected to the rear portion of a tractor to carry out tilling.

The invention uses the following technical means.

That is, according to a first aspect of the invention, a tractor comprises a traveling vehicle body having a pair of front wheels19and a pair of rear wheels11, an engine2that is mounted to the front portion of said traveling vehicle body and has an output shaft2a,a transmission case3that is disposed at the rear portion of the traveling vehicle body and houses a transmission including an input shaft5and a front wheel driving shaft13, a first universal joint6joining the output shaft2aof the engine2and the input shaft5of the transmission case3, a work machine24attached between the front wheels19and rear wheels11so as to enable it to rise and fall, a front axle housing14supporting the pair of front wheels19, a front wheel traveling input shaft15projected rearward to the inclined upper side at the rear portion of the front axle housing14, and a second universal joint17joining the front wheel traveling input shaft15and a front wheel driving shaft13projecting from the transmission case3.

According to a second aspect of the invention, the abovementioned work machine24mounted to the tractor is a mower for mowing.

According to a third aspect of the invention, the tractor according to the first or second aspect of the invention is constructed so that the first universal joint6is provided at the horizontal center of the traveling vehicle body in a planar view, the second universal joint17is provided so as to deflect horizontally with respect to this first universal joint6, and the first universal joint6is provided higher than the second universal joint17when it is viewed from the side.

Action of the abovementioned construction is as follows.

A driving force from the front wheel driving shaft13is transmitted to the front wheel traveling input shaft15via the second universal joint17to drive the front wheels19supported by the front axle housing14.

During work, a rotating drive force is transmitted to the drive part of the work machine (mower24) from the mid PTO shaft at the transmission case3side or the front PTO shaft21at the engine front portion to rotate the drive part, and this force lifts the work machine when the tractor travels across a farm field or on a road after finishing the work.

In this case, the rear end of the front wheel traveling input shaft15which projects rearward to the inclined upper side from the rear portion of the front axle housing14is at a high position from the ground, and this front wheel traveling input shaft15and the front wheel driving shaft13at the transmission case3side are joined by the second universal joint17. Therefore, the second universal joint17itself can be provided at a high position, and is prevented from obstructing lifting of the work machine (mower24), so that a lifting and lowering space for the work machine can be widely secured between the front wheels19and the rear wheels11.

Particularly, since the second universal joint17is provided so as to deflect horizontally, a mower24having a gearbox projecting upward on the upper surface of the work machine (mower24) can be lifted high.

In the construction of the abovementioned Japanese Unexamined Patent Publication No. H09-272350, a mower lifting space is secured while a driving force from the transmission is transmitted to a first middle shaft horizontally disposed, a bearing supported by the traveling frame, the second middle shaft whose the front side hangs down and which is connected to said bearing, a gear mechanism, and then an input shaft for front wheel driving. On the other hand, according to the invention, as mentioned above, in a construction obtained by only joining the front wheel traveling input shaft15projecting rearward to the inclined upper side from the rear portion of the front axle housing14and one long middle shaft (second universal joint)17to each other, a mower lifting space can be secured while a driving force from the transmission3is transmitted to the traveling input shaft15.

The front wheel traveling input shaft15is joined by one long middle shaft (second universal joint)17, and the angle formed by crossing the shafts15and17with each other become smaller, so that the structure strength is prevented from deteriorating, and a mower lifting space can be secured by a relatively small number of parts (only the second universal joint17is used as a middle shaft in place of the first and second middle shafts in the construction of Japanese Unexamined Patent Publication No. H09-272350, and furthermore; no bearing and gear mechanism are used).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the invention will be described with reference to the accompanying drawings. First, describing the construction, an engine2is mounted to the front portion of the body of the tractor1, and a rotating drive force of this engine2is transmitted to a pump shaft5of a hydrostatic transmission (HST) mounted to the front portion of a transmission case3via a first universal joint6.

In the case of a tractor that comprises no hydrostatic transmission (HST), the rear end of the first universal joint6is directly joined to a transmission input shaft provided at the front portion of the transmission case3, however, the tractor1of the present embodiment includes a hydrostatic transmission (HST)4mounted to the front portion of the transmission case3, so that the first universal joint6is joined to the pump shaft5of the hydrostatic transmission (HST)4.

A rotating drive force inputted into the hydrostatic transmission (HST)4is controlled so as to control the number of revolutions and the direction of rotation of a motor shaft10in accordance with a pressing degree of an HST pedal9provided on the right of the floor8by changing the inclination angle of the swash plate of HST.

The rotating drive force of the motor shaft10is reduced by a sub-transmission inside the transmission case3, which is not shown, and a part of the force is transmitted to the rear wheel axle12via a differential gear to drive the rear wheels11, and a driving force that diverges in the front of the differential gear is transmitted to the front wheel driving shaft13. The front wheel driving shaft13is provided so as to project forward on the right of the front face of the transmission case3, and this front wheel driving shaft13and the front wheel traveling input shaft15pivotally supported on the rear portion of the front axle housing14are interlocked and joined to each other via a second universal joint17that is longitudinally long to drive the front wheels19.

More concretely, the front axle housing14is supported so as to swing around a center pivot37along the longitudinal direction, and to the rear right portion of the front axle housing14, a holder case16to hold the front wheel traveling input shaft15is detachably attached.

The holder case16is diagonally attached to the front axle housing14so that the rear end thereof faces upward in an inclined backward direction, the front wheel traveling input shaft15is pivotally supported on this holder case16, and the front end of the second universal joint17is joined to the rear end of this front wheel traveling input shaft15.

To the rear end of the holder case16, a cylindrical rubber cover20is attached to prevent entry of mud and dust.

Furthermore, at two points of the front and rear lower portions of the transmission case3, a mid PTO shaft21and a rear PTO shaft22are respectively laid, and a rotating drive force is transmitted to these via the transmission inside the transmission case3and a PTO clutch23.

The rear PTO shaft22is used for driving a work machine such as a rotary tiller (not shown) connected to the rear portion of the tractor1, and the mid PTO shaft21is provided between the front wheels19and the rear wheels11and used for driving a work machine such as a mower24mounted on the lower body portion of the tractor1.

This mid PTO shaft21is provided on the first universal joint6at the opposite side (on the left in the traveling direction) of the second universal joint17in a planar view.

The mower24is connected to the traveling vehicle body by a link mechanism25in a manner enabling it to rise and fall, and an input shaft28projecting rearward from a gear box26of the mower24and the mid PTO shaft21are interlocked and joined to each other by a third universal joint29to rotate a plurality of blades30inside the mower24. The link mechanism25for lifting and lowering the mower24may be driven by a hydraulic cylinder or an electric motor, however, in this embodiment, a feedback link mechanism27is connected to the end of the lift arms38to lift and lower the mower24in accordance with movements of the lift arm38.

When the lift arms38rotate, the mower24rises and falls roughly parallel to the ground. A gear pump31is attached to the front portion of the transmission case3, and a control valve33for lifting and lowering the work machine is detachably attached to the upper portion of this gear pump31. On the other hand, a hydraulic cylinder case36housing a single-acting hydraulic cylinder34is provided on the upper portion of the transmission case3, and to both the right and left sides of the hydraulic cylinder case3, lift arms38and38are rotatably pivotally attached. The gear pump31is always driven via the gear inside the transmission case3, which is not shown. The gear pump31and the bottom of the transmission case3are connected via the suction pipe32so that hydraulic oil serving also as transmission oil inside the transmission case3is suctioned into the gear pump31via this suction pipe32.

Furthermore, the tractor1shown inFIG. 1is provided with an operating lever40for turning on and off the PTO clutch, an operating lever41for lifting and lowering a work machine, a seat42, a steering handle43, a full hydraulic power steering unit44, and a power steering hydraulic cylinder45, and a safety frame47is provided at the rear portion of a chassis46of the tractor1.

Next, construction of the entire hydraulic system will be described based on the hydraulic circuit diagram shown in FIG.4.

A control valve33placed at the upper portion of the gear pump31is formed by integrally installing a main relief valve49, a flow dividing valve50, and a main spool52inside, and most of the hydraulic oil is fed to the main spool52side of the hydraulic lifting and lowering system by the flow dividing valve50, and the residual hydraulic oil is fed to the power steering unit44side through a piping53. The main spool52is slidably fitted with the control valve33, and the hydraulic lifting and lowering operating lever41is rotated forward and rearward to slide the main spool52in the lengthwise direction. For the main spool52, “lifting position”, “neutral position”, and “lowering position” are set, and when it is set to the “lifting position”, the hydraulic oil is fed into the hydraulic cylinder34through a piping54to rotate the lift arms38to the lifting side.

By attaching a cover member55including an oil passage formed inside to the control valve33, the flow dividing valve50side and the main spool52side are communicated with each other through the oil passage80, and when this cover member55is removed, an oil passage60for external hydraulic discharge is formed, and when external hydraulic equipment such as a valve of a front loader is connected hereto, the external equipment becomes operable.

In the full hydraulic power steering unit44, the valve44ais switched by the steering handle43, the hydraulic oil is fed into the power steering hydraulic cylinder45, and the piston rod45amoves laterally to steer the front wheels19.

The returning side of the power steering unit44is connected to the PTO valve63via a piping61, and when this PTO valve63switches to on by the PTO operating lever40, connection to the PTO clutch23is made and the mid PTO shaft21and the rear PTO shaft22rotate. In the present embodiment, by operating a shifter inside the transmission case3, the mid PTO shaft21and the rear PTO shaft22can be independently rotated or simultaneously rotated.

The oil passage formed by branching the middle of the piping61is connected to the hydrostatic transmission (HST)4via a PTO relief valve65and a charge filter66in this order.

The hydrostatic transmission (HST)4is provided with a low pressure relief67and a high pressure relief68. In response to drive of the HST pump7, the HST motor18is driven and the tractor1travels.

Next, the constructions of FIG.5throughFIG. 7will be briefly described.

FIG. 5is a drawing of the periphery of the hydrostatic transmission (HST)4when being viewed from the front, and at the horizontal inner ends of the control valve33positioned below the left side of the seat42, a rotary shaft70for sliding the main spool52is projectedly provided horizontally inward, an extending shaft71is attached to this rotary shaft70, and the lower end of the hydraulic lifting and lowering operating lever41positioned at the right side of the seat42is attached to the end of the extending shaft71.

Thus, since the extending shaft71is attached to the rotary shaft70that slides the main spool52and a hydraulic lifting and lowering operating lever41is directly attached to this extending shaft, in comparison with a system in which a link is interposed as in the prior art, operations become smooth and extra parts becomes unnecessary, and this can suppress manufacturing costs.

FIG. 6is a drawing showing the hydrostatic transmission (HST)4and the transmission case3viewed from the side, andFIG. 7is a plan view of the same, wherein a cooling fan72is attached to the front of the pump shaft5of the hydrostatic transmission (HST)4, and during drive of the engine, the main body of the hydrostatic transmission (HST)4is cooled by this cooling fan72. The hydraulic oil at the returning side of the full hydraulic power steering unit44reaches the PTO valve63through the piping61, a valve rotary shaft74is switched by rotating the PTO operating lever40, whereby the hydraulic oil is guided to the PTO clutch23or discharged to turn the PTO clutch23on/off.

Next, the construction of the control valve33will be described based on FIG.8through FIG.11.FIG. 8is a plan sectional view of the control valve, and on the left side of the valve body33A, a main relief valve49and a flow dividing valve50are provided forward and rearward at a predetermined space. A high-pressure hydraulic oil fed from the gear pump31enters a valve chest50aof the flow dividing valve50through a hole98made in the valve body33A, and a part of the hydraulic oil moves toward the full hydraulic power steering unit44through the piping53from an outlet port76.

A hole78at the flow dividing valve50side and a through hole79at the main spool52side are communicated by an oil passage80formed in the cover member55, and the oil passage is properly switched by sliding of the main spool52, whereby the hydraulic oil that has entered the main spool52flows into the hydraulic cylinder34inside the hydraulic cylinder case36through the piping54from an outlet port82. Concretely, when the hydraulic lifting and lowering operating lever41is turned rearward and the main spool52is slid forward (leftward in FIG.8), a semicircular small opening84formed in the main spool52is communicated with a chamber85at the lifting side, and the hydraulic oil enters the chamber85through the opening84and flows into the hydraulic cylinder34through the outlet port82.

On the other hand, when the hydraulic operating lever41is turned forward and the main spool52is moved rearward (rightward in FIG.8), the hydraulic oil that has flown in the hydraulic cylinder34enters the chamber85through the same piping54, passes through the small opening84a,and returns to the transmission case3that is a hydraulic tank.

The hole86and the hole89of the main spool52are always communicated with each other, the hole89is communicated with an unloading port87, and the unloading port87is communicated with the transmission case3through the piping94.

The relationship between the main spool52and the control valve33will be described in detail with reference toFIG. 9,FIG. 10, and FIG.11. These figures show the section of the control valve33when being viewed from the right side, whereinFIG. 8is a sectional view when the main spool52is at a neutral position,FIG. 9is a sectional view when the main spool52is at a lowering position, andFIG. 11is a sectional view when the main spool52is at a lifting position.

At the front end outer circumference of the rotary shaft70which slides the main spool52forward and rearward, a positioning notched portion91is formed, and a steel-made detent ball93pressed by the spring92enters this notched portion91to hold the neutral condition of the main spool52.

At the inner end of the rotary shaft70, a shifter95is fixed downward so as to slide the main spool52, and the lower end of the shifter95is fitted into a concavity96formed at the upper portion of the main spool52.

The main spool52has three large diameter portions52A,52B, and52C and two small diameter portions52dand52ein the lengthwise direction. When the main spool52is in the neutral condition, the chamber97into which the high-pressure hydraulic oil flows in from the gear pump31and the adjacent chamber90are communicated with each other, whereby the hydraulic oil flows into the chamber90side from the chamber97, and the condition changes into a so-called unload condition where all of the hydraulic oil flows enters the transmission case3. At the rear side of the chamber90, a damper chamber99that is communicated with this chamber90and has an inner diameter slightly larger than that of the large diameter portion52C of the main spool52is formed.

This damper chamber99applies a resistance at the moment the large diameter portion52C of the main spool52slips into the damper chamber99when the hydraulic operating lever41is pushed down to slide the main spool52rearward (leftward in FIG.10), whereby a load change is conveyed to an operator who operates the hydraulic lifting and lowering operating lever41, and it is possible to make the operator recognize that this pushing-down operation effectively acts.

When the hydraulic operating lever41is operated to the lowering side, the hydraulic oil inside the hydraulic cylinder34returns to the inside of the transmission case3through the piping54, the chamber85, the opening,84a,the holes86and89, the port87, and the piping94in order.

On the other hand, when the hydraulic operating lever41is operated to the lifting side, the main spool52moves forward (rightward in FIG.11), and the large diameter portion52C at the rear end of the main spool52intercepts the communication between the chambers90and97. Then, the high-pressure hydraulic oil from the gear pump31enters the inside of the chamber85through the opening84and flows into the hydraulic cylinder34through the outlet port82and the piping83to lift the lift arms38.

According to the first aspect of the invention, a sufficient work machine lifting and lowering space can be secured between the front wheels19and rear wheels11, and a work machine mounted to the lower portion of the traveling vehicle body can be lifted high from the ground, whereby movements of the traveling vehicle body can be made easier.

Furthermore, the second universal joint17for driving the front wheels19is constructed so that the middle portion is not supported on the vehicle body via a bearing but is directly joined to the front wheel traveling input shaft15that is provided so as to project rearward to the inclined upper side, so that the second universal joint17can also be provided at a high position from the ground, a work machine lifting and lowering space can be sufficiently secured, the construction becomes simpler, and the number of parts is reduced, whereby manufacturing at low cost is realized.

Particularly, as in the second aspect of the invention, when a mower is mounted as a work machine, there is no possibility that a gear box and the like for driving the mower blades come into contact with the second universal joint17, so that the tractor can travel by lifting the mower high.

Moreover, according to the third aspect of the invention, a rotating drive force of the engine2is smoothly transmitted to a driving force transmitting part at the transmission case3side without hindrance, and driving force transmission to the front wheels19is reliably achieved by the second universal joint17passing a high position from the ground, and therefore, when a work machine is mounted between the front and rear wheels19and11, the machine can be lifted high without any problem.

According to the fourth aspect of the invention, the control valve33is constructed so as to include the work machine lifting and lowering main spool52and the flow dividing valve50for feeding a part of the hydraulic oil to the work machine lifting and lowering hydraulic cylinder34and feeding the residual oil to other hydraulic equipment44, which are integrally installed, and this control valve33is attached to the upper portion of the gear pump31that is driven by a driving force from the transmission case3, and the hydraulic operating lever41for operating the main spool52is attached to the shaft70projecting horizontally sideward from the control valve33, so that switching of the valve33is smoothly carried out, and since the control valve33and the gear pump31can be joined to each other without using a piping, reliable operations while pressure breakage is prevented can be expected. In addition, since the control valve33and the gear pump31are collectively provided above the transmission case3, assembly and disassembly can be easily carried out.

Furthermore, according to the fifth aspect of the invention, since an external hydraulic extracting port60is formed in the side surface of the control valve33, the front loader and other work machines can be hydraulically driven.

Furthermore, according to the sixth aspect of the invention, a damper chamber99is provided between the end at the lowering position side of the main spool52and the control valve body33A side to provide a damper effect in the minute lowering region for starting lowering of the work machine, so that movements of the hydraulic operating lever41for operating the main spool52when starting a lowering operation can be made smooth, and for example, fine adjustments in tilling depth of a rotary cultivator can be easily made.