JP4871032B2 - Steering structure of work equipment - Google Patents

Description

  The present invention relates to a steering operation structure used for a four-wheel traveling type working machine.

As a steering operation structure of a rice transplanter which is an example of the above working machine, for example, as disclosed in Patent Document 1, a mission case provided in the front part of the aircraft is equipped with a steerable front wheel, The lower part of the steering shaft that is inserted and supported in the vertical direction and the steering mechanism of the front wheels are linked together, and the hydraulic pump for supplying working hydraulic oil is driven by the pump drive shaft that is linked and linked to the engine. Is known.
JP 2000-272359 A

  The conventional structure has the feature that the steering shaft can be reliably supported with a large span that effectively uses the vertical height of the transmission case, but the pump drive shaft is disposed outside the front of the transmission case. Therefore, the shaft support part that penetrates and supports the input shaft of the hydraulic pump is exposed to the outside, and a strict oil seal structure is required to prevent oil leakage from this shaft support part. It was.

  In order to connect the input shaft and the pump drive shaft of the hydraulic pump concentrically, the input shaft and the pump drive shaft are often inserted into a connecting sleeve and connected by spline. In this case, oxidation wear at the spline fitting portion is reduced. In order to prevent this, it is desirable to frequently fill with grease. However, since this spline fitting portion is a narrow portion inside the body, the grease filling tends to be omitted or forgotten.

  The present invention has been made paying attention to such points, and has as its main object to enable a hydraulic pump to be suitably driven without the above problems.

With the first invention, equipped with a steerable front wheel to a transmission case that is deployed in body front interlockingly connected to the lower and front wheel steering shaft inserted through the bearing in the vertical direction in the transmission case, the engine In a steering operation structure of a working machine configured to drive a hydraulic pump that supplies hydraulic oil for working with a pump drive shaft that is linked and linked to the
The input shaft of the hydrostatic continuously variable transmission connected to the side of the transmission case is linked to the engine, the output shaft of the hydrostatic continuously variable transmission is linked to the transmission system in the transmission case, Connecting the input shaft and the pump drive shaft concentrically;
The steering shaft is arranged in an up and down direction in a tilted posture so as to be along a front wall portion of the transmission case that is inclined so that the lower side is positioned on the front side from the upper side. The pump drive shaft is inserted and supported in the transmission case in the case behind the steering shaft so that the steering shaft and the pump drive shaft are close to each other ,
A rotating shaft having a pitman arm for steering the front wheel is provided on the rear side below the steering shaft in parallel with the steering shaft, and the front end portion of the pitman arm is located behind the front end portion of the transmission case. In the transmission case, the pinion gear below the steering shaft and the sect gear of the rotating shaft are engaged with each other, the pitman arm is swung by the steering shaft, and the front wheel is It is configured to be steered .

  According to the above configuration, the input shaft shaft support portion of the hydraulic pump can be communicated with the inside of the transmission case, and even if leakage oil from the hydraulic pump flows out of the shaft support portion, it leaks out of the machine only by flowing into the transmission case. There is nothing.

Since the connecting part between the pump drive shaft and the input shaft of the hydraulic pump can be arranged in the transmission case, the connecting part should be located in an atmosphere where many splashes of lubricating oil are scattered or immersed in the lubricating oil. Even if the pump drive shaft and the input shaft of the hydraulic pump are splined together, the spline fitting portion can be always lubricated.
The input shaft of the hydrostatic continuously variable transmission can be used as a transmission shaft for transmitting power from the engine to the pump drive shaft, and the transmission structure from the engine to the pump drive shaft can be simplified.

  Therefore, according to the first invention, the rational arrangement improvement of the pump drive shaft can simplify the oil seal structure in the input shaft shaft support portion in the hydraulic pump, and the pump drive shaft and the input shaft of the hydraulic pump Lubrication maintenance of the connecting part can be made unnecessary.

According to a second invention, in the first invention,
A steering handle disposed above the transmission case and the steering shaft are disposed concentrically.

According to the above configuration, while pivotally to the inclined posture collapse after easily operate the steering wheel, can be interlocked without intervention of the universal joint and the steering wheel and the steering shaft, with leads to the effect of the first aspect of the present invention Thus, the steering operation structure can be simplified.

According to a third invention, in the first or second invention,
The steering shaft is driven and rotated by a torque generator.

According to the said structure, while bringing the said effect of 1st or 2nd invention, a light front wheel steering can be performed.

A fourth invention, in any one invention of the first to 3
With mounting the engine in the previous frame extending forward from the transmission case, in which are provided with a contact portion for restricting the maximum steering angle of the front wheels to the front frame.

According to the above configuration, resulting in the effect of any one invention of the first to 3 can be the front wheel is excessively being steered to prevent the steering mechanism may be damaged.

  1 and 2 show a side surface and a plane of a riding type rice transplanter as an example of a working machine. This rice transplanter is a 6-row planting seedling as a working device at the rear of a four-wheel drive type traveling machine body 3 having a pair of left and right front wheels 1 that can be steered and a pair of left and right rear wheels 2 that cannot be steered. The planting device 4 has a basic structure in which a vertical quadruple link mechanism 6 driven by a hydraulic cylinder 5 is connected so as to be movable up and down, and a fertilizer device 7 is provided at the rear of the machine body.

  A transmission case 9 that pivotally supports the front wheel 1 is connected and fixed to the front part of the body frame 8 in the traveling body 3, and a rear transmission case 10 that is equipped with the rear wheels 2 on the left and right at the rear part of the body frame 8. Is supported so that it can roll. A front frame 11 extends forward from the mission case 9, and an engine 12 is mounted horizontally on the front frame 11 and covered with a hood 13. The boarding driving part located behind the engine 12 is provided with a steering handle 14 for steering the front wheel 1, a driving seat 15, a step 16, and the like. Preliminary seedling raising bases 17 are provided for placing and accommodating in stages.

The seedling planting device 4 mounts six mats of seedlings in parallel and cuts out seedlings one by one from the lower end of the seedling platform 21 and the seedling platform 21 that are reciprocated by a predetermined stroke in the left-right direction. It comprises six sets of rotary planting mechanisms 22 that are planted on the surface, three leveling floats 23 that are arranged in parallel to level the planting location of the field T , and the like.

The main part of the fertilizer application device 7 is mounted on the traveling machine 3 between the driver's seat 15 and the seedling planting device 4, and a fertilizer hopper 24 for storing powdered fertilizer and a fertilizer in the fertilizer hopper 24 are set. Rotating roll type feeding mechanism 25 that feeds out by quantity, electric blower 28 that winds fed fertilizer to groove forming device 27 provided in each leveling float 23 via supply hose 26, and the like. The fertilizer is fed into a groove formed on the surface T and buried.

3 and 4 schematically show the transmission system.
A main transmission 30 consisting of a hydrostatic continuously variable transmission (HST) is connected to the left side surface of the mission case 9 and is linked to the engine 12 by a belt. The output of the main transmission 30 is connected to the mission case 9. Is branched into a traveling system and a working system. The power of the branched traveling system is transmitted to the front wheels 1 and the rear wheels 2 via the gear-type sub-transmission mechanism 31, and the power of the branched working system is transmitted to the gear-type PTO transmission mechanism (inter-company transmission mechanism) 32 and The PTO clutch (planting clutch) 33 is taken out rearward from the PTO shaft 34, and the extracted power is transmitted to the seedling planting device 4 via the transmission shaft 35a and the expansion / contraction transmission shaft 35b.

  The main transmission 30 has a variable displacement hydraulic pump P that can switch the pressure oil discharge direction between forward and reverse and can change the discharge amount steplessly, and is driven to rotate by receiving pressure oil from the hydraulic pump P. A fixed displacement hydraulic motor M is built in, and an input shaft (pump shaft) 36 for driving the hydraulic pump P is driven in a belt-linked manner with the engine 12, and an output shaft (pump shaft) of the hydraulic motor M is driven. ) The speed change power taken out from 37 is transmitted to the mission case 9.

  The main transmission 30 is linked to a main transmission lever 18 that can be swung back and forth on the left side of the steering handle 14 and can be held at an arbitrary operation position, so that the main transmission lever 18 is in a neutral position. By operating, the amount of pressure oil discharged from the hydraulic pump P becomes zero and traveling is stopped, and by operating the main transmission lever 18 forward from the neutral position, pressure oil is discharged from the hydraulic pump P in the positive direction. Thus, the continuously variable transmission in the forward direction is performed, and by operating backward from the neutral position, the hydraulic oil is discharged in the reverse direction from the hydraulic pump P, and the continuously variable transmission in the backward direction is performed.

  A portion of the power input to the transmission case 9 is shifted to the differential gear 38 by the auxiliary transmission mechanism 31 and then transmitted to the differential gear 38. The differential gear 38 is branched to the left and right differential shafts 39 to be shifted to the front wheels 1 Is transmitted to. A part of the power transmitted to the differential device 38 is branched by the bevel gear, taken out of the case from the rear wheel drive shaft 40, and transmitted to the rear transmission case 10 via the transmission shaft 41 arranged along the lower part of the fuselage. Then, it is transmitted to the left and right rear wheels 2 via the multi-plate type side clutch 42.

  The differential device 38 includes a differential lock mechanism 43 that integrates the left and right differential shafts 39. The diff lock mechanism 43 is linked to a diff lock pedal 44 provided at the rear portion of the foot, and the left and right front wheels 1 can be driven at a constant speed by depressing the diff lock pedal 44. Yes. The rear wheel drive shaft 40 is equipped with a multi-plate brake 45, and the brake 45 is linked to a brake pedal 46 disposed at the right front position of the foot, and the rear wheel drive is performed by depressing the brake pedal 46. By braking the shaft 40, the entire traveling system is braked, and the front wheel 1 and the rear wheel 2 can be braked simultaneously. The brake pedal 46 is also linked to the operation system of the main speed change lever 18, and when the brake pedal 46 is depressed, the main speed change lever 18 in the forward shift range or the reverse shift range is forcibly returned to the neutral position. It is like that.

  Although the detailed structure is not shown, the left and right side clutches 42 are automatically operated in conjunction with the steering of the front wheels 1, and the steering wheel 14 moves the front wheels 1 to the left or right at a set angle (for example, 30 °). ) When steered as described above, the side clutch 42 of the rear wheel 2 that is on the inside of the turn is automatically turned off, and a small turn is performed by three-wheel drive with the left and right front wheels 1 and the rear wheel 2 on the outside of the turn. It is like that.

Details of the internal structure of the mission case 9 are shown in FIGS.
The transmission case 9 is constructed by bolting left and right divided case portions 9a, 9b made of aluminum die cast, and an input transmission shaft 50 mounted horizontally on the transmission case 9 is a main transmission 30. The output shaft 37 is concentrically connected. A transmission shaft 50 that is driven to rotate by being continuously variable in the forward and reverse directions in response to an output from the main transmission 30 and a traveling system transmission shaft 51 that is supported in parallel with the transmission shaft 50 are connected via the auxiliary transmission mechanism 31. Linked together.

  The subtransmission mechanism 31 includes large and small gears G1 and G2 fixed to the left half of the transmission shaft 50, and a shift gear SG splined to the traveling transmission shaft 51. The shift gear SG is shown in FIG. In FIG. 5, the gear G3 is shifted to the right and the large gear G3 is engaged with the gear G2, thereby bringing about a "low speed". The shift gear SG is shifted to the left in FIG. 5 and the small gear G4 is moved to the gear G1. Engagement results in a “high speed”, and the speed change power is extracted from the output gear G5 fixed to the right end of the speed change shaft 51. The shift operation shaft 52 that shifts the shift gear SG of the subtransmission mechanism 31 is pushed and pulled by a front / rear swing operation of the subtransmission lever 19 that is provided on the left side of the driver seat 15 so as to swing back and forth. It has become.

  A differential gear case 53 in the differential device 38 for driving the front wheels is supported by a bearing below the transmission case 9, and a large-diameter input gear G 6 fixed near the right end of the differential gear case 53 is an output of the traveling system transmission shaft 51. The gear G5 is engaged with the gear G5, and the transmission power from the subtransmission mechanism 31 is greatly decelerated and transmitted to the differential device 38. The differential lock mechanism 43 is configured so that the left and right differential shafts 39 are integrally rotated by engaging a shift collar 54 key-coupled to the left differential shaft 39 with a left end portion of the differential gear case 53. A differential lock operating shaft 55 for shifting the shift collar 54 is linked to the differential lock pedal 44.

  A bevel gear G7 fixed to a position near the right end of the differential gear case 53 and a bevel gear G8 formed integrally with the front end of the rear wheel drive shaft 40 are engaged with each other, and a part of the driving power transmitted to the differential device 38 is rearward. It is taken out from the wheel drive shaft 40. The brake 45 mounted on the rear wheel drive shaft 40 includes a plurality of friction plates 57 that are externally splined to the rear wheel drive shaft 40, and the friction plates 57 that are non-rotatably engaged and supported on the inner surface of the case. The brake plate 56 includes a plurality of alternately stacked brake plates 56 and a press collar 58 that is fitted to the rear wheel drive shaft 40 so as to be shiftable. The friction plate 57 and the brake plate are operated by shifting the press collar 58 forward. The rear wheel drive shaft 40 is frictionally braked by pressure-contact polymerization with 56.

  A rotation operation shaft 59 for shifting the pressing collar 58 back and forth is linked to the brake pedal 46. When the brake pedal 46 is not depressed, the pressing collar 58 is released from the pressing force by the return urging force of the brake pedal 46. The pressing collar 58 is pressed and shifted by retracting to the position and depressing the brake pedal 46 against the return urging force. This rotation operation shaft 59 is inserted and supported from the right lateral outer side to the bearing boss portion 9e of the left divided case portion 9a in the transmission case 9, and is a contact portion integrally protruding from the right divided case portion 9b. As 9c approaches the outer end of the rotation operation shaft 59 and is disposed opposite to it, the extraction of the rotation operation shaft 59 is prevented.

  A PTO transmission member 60 is fitted on the right half of the transmission shaft 50. The PTO transmission member 60 includes a boss portion 62 that is externally fitted to the transmission shaft 50 via a one-way clutch 61, and an output portion 63 that is loosely fitted to the transmission shaft 50. The output part 63 is nail-engaged from the axial direction at the left end, and the boss part 62 and the output part 63 are integrally rotated. The one-way clutch 61 has a characteristic of transmitting only the forward rotation power of the transmission shaft 50 to the boss portion 62, and only the forward rotation power of the transmission shaft 50 that rotates forward and reverse is transmitted from the output portion 63 of the PTO transmission member 60. It is taken out and transmitted to the PTO transmission mechanism 32.

  The PTO transmission mechanism 32 includes a cylindrical shaft-shaped intermediate transmission shaft 64 that is loosely supported by the right half of the traveling system transmission shaft 51, an input portion 65 that is externally fitted and fixed to the intermediate transmission shaft 64, and an intermediate transmission shaft 64. A plurality (six in this example) of drive-side gears G11 to G16 that are externally fitted and fixed in parallel, a PTO transmission shaft 66 that is supported in parallel with the traveling transmission shaft 51, and the PTO transmission shaft 66 A plurality of driven gears G17 to G22, etc., which are loosely fitted in parallel and always meshed with each of the drive side gears G11 to G16, are formed.

  The input portion 65 is located at the end of the PTO transmission mechanism 32 on the inner side of the case, and is disposed to face the output portion 63 of the PTO transmission member 60, and has a small-diameter output gear G9 formed in the output portion 63. The large-diameter input gear G <b> 10 formed in the input unit 65 is interlocked and interlocked so that the normal rotation power of the PTO transmission member 60 is decelerated and transmitted to the intermediate transmission shaft 64 of the PTO transmission mechanism 32.

  The right half of the PTO transmission shaft 66 that loosely supports the driven gears G17 to G22 is formed in a cylindrical shaft portion 66a, and can be displaced in and out in the radial direction at each gear mounting position of the cylindrical shaft portion 66a. A plurality of transmission balls 67 are engaged with each other in the circumferential direction. The transmission ball 67 immerses inward from the outer periphery of the cylindrical shaft portion 66a, thereby allowing the driven-side gears G17 to G22 mounted on the outer fit to freely rotate, and the transmission ball 67 projects from the outer periphery of the cylindrical shaft portion 66a. By engaging with a large number of engaging recesses 68 formed along the inner periphery of the side gears G17 to G22, the driven side gears G17 to G22 and the PTO transmission shaft 66 are in a transmission state in which they rotate together. The PTO system transmission shaft 66 can be shifted to six stages by selecting any one of the six driven gears G17 to G22 and selecting the transmission state. It has become.

  A shift operation shaft 69 is inserted through the center of the cylindrical shaft portion 66a of the PTO transmission shaft 66 so as to be reciprocally movable in the axial direction. The outer diameter of the speed change operation shaft 69 is formed to have a small diameter so as to form a space sufficient for the transmission ball 67 to fall inward from the outer periphery of the cylindrical shaft portion 66a and retract, and the case of the speed change operation shaft 69. A large-diameter portion 69a slidably in contact with the inner periphery of the cylindrical shaft portion 66a is attached to the inner end portion in a flange shape, and six sets are arranged in parallel in the axial direction by shifting the speed change operation shaft 69. One set of the transmission balls 67 is pushed and displaced to the outer periphery by the large-diameter portion 69a, so that one set of six normally-engaged gear pairs is set in the transmission state, and the intermediate transmission shaft 64 is transferred to the PTO transmission shaft 66. Power transmission is performed at a desired transmission ratio.

  Six annular grooves 70 are formed in parallel on the speed change operation shaft 69 at a pitch corresponding to the gear parallel pitch, and a detent ball 71 engaged with one of the annular grooves 70 is formed on the wall portion of the transmission case 9. Is installed so that the shift operation shaft 69 is stably held at each of the selected six shift operation positions.

  The output bevel gear G23 connected and fixed to the left end portion of the PTO transmission shaft 66 and the input bevel gear G24 loosely fitted to the PTO shaft 34 are engaged, and the working power transmitted to the input bevel gear G24 is transmitted to the PTO clutch. It is transmitted to the PTO shaft 34 via 33.

  The PTO clutch 33 includes a driving side clutch member 72 connected to the input bevel gear G24, a driven side clutch member 73 slidably mounted on the PTO shaft 34, and the driven side clutch member 73 as a driving side clutch member. The pawl clutch is provided with a clutch spring 74 that slidably urges toward 72. The driven-side clutch member 73 is slid and biased by the drive-side clutch portion 72, thereby bringing about a “clutch-on” state in which power is transmitted from the drive-side clutch member 72 to the PTO shaft 34. The clutch member 73 is slid backward against the clutch spring 74, thereby bringing about a “clutch disengagement” state in which power transmission from the drive side clutch member 72 to the PTO shaft 34 is interrupted.

  The driven clutch member 73 is formed with an inclined cam 75 whose height in the axial direction changes depending on the rotation phase, and the clutch operating shaft 76 can be slid inward and outward on the side of the PTO clutch mounting portion. Has been deployed. As shown in FIG. 6, when the clutch operating shaft 76 is retracted outward, the driven clutch portion 73 is slid and biased to bring about the “clutch engaged” state. Is pushed in, the tip of the clutch operating shaft 76 enters the rotation locus of the inclined cam 75, and the inclined cam 75 rides on the clutch operating shaft 76 whose axial center position is fixed. Due to the climbing cam action of the shaft 76 and the inclined cam 75, the driven side clutch member 73 is forcibly retracted against the clutch spring 74 with its rotation, and a “clutch disengaged” state in which the claw engagement is disengaged. Brought about.

  The PTO clutch 33 configured as described above has a fixed position stop function in which the driven-side clutch member 73 is brought into a “clutch disengaged” state at a predetermined rotational phase. In this “clutch disengaged” state, The rotation phase of the PTO transmission system is set so that the mechanism 22 stops at the rotation phase rising from the surface T.

  As shown in FIGS. 5 and 9, a hydraulic pump 77 serving as a hydraulic source such as the hydraulic cylinder 5 and power steering means described later is connected laterally to the front right side surface of the transmission case 9. A pump drive shaft 78 for driving the hydraulic pump 77 is disposed laterally in the mission case 9. One end of the pump drive shaft 78 is splined concentrically with the extension end in the case of the input shaft 36 in the main transmission 30 via a connection sleeve 79, and the other end of the pump drive shaft 78 is input to the hydraulic pump 77. The shaft 80 is splined concentrically via a connecting sleeve 81, and the hydraulic pump 77 is driven by engine power input to the main transmission 30.

As shown in FIGS. 8 and 9 , a hydraulic torque generator 85 for power steering is connected to the front upper surface of the transmission case 9 in a slightly tilted posture, and the steering is extended upward from the torque generator 85. The steering handle 14 is connected to the upper end of the operation shaft 86. An output shaft 87 that is hydraulically torqued up from the lower surface of the torque generator 85 is projected with the same backward tilt angle as the steering operation shaft 86, and a steering shaft 88 concentrically connected to the output shaft 87 is provided. The steering handle 14, the steering operation shaft 86, and the steering shaft 88 are arranged concentrically on a straight line that is tilted backward and is inserted into the transmission case 9 in front of the pump drive shaft 78.

A rotation shaft 89 is provided through the front bottom wall of the transmission case 9, and a sect gear 90 connected to a case inner portion of the rotation shaft 89 and a pinion gear 91 integrally formed at the lower end portion of the steering shaft 88 are engaged. together we are, pitman arm 92 for the front wheels steering is connected to the case outer end portion of the rotary shaft 89, tie rods 93 issued pivot支延from the free end on the left and right of the pitman arm 92, left and right front wheels 1 Is connected to a knuckle arm 1a. As shown in FIG. 11, the contact ends 92a formed at the left and right ends of the pitman arm 92 are received by the left and right ends of the contact portion 11a projecting downward from the base portion of the front frame 22, so that the front wheel 1 The maximum steering angle to the left or right is limited.

  As shown in FIG. 9, an oil filter 95 is attached to the right side surface of the mission case 9. As shown in the hydraulic circuit diagram of FIG. 10, the lubricating oil stored in the transmission case 9 is introduced into the oil filter 95 as hydraulic oil, and the purified hydraulic oil is passed through an oil passage a formed in the case wall. The hydraulic oil sucked by the hydraulic pump 77 and pressurized and discharged by the hydraulic pump 77 is supplied to the torque generator 85 via the external pipe 96. The return oil sent out from the torque generator 85 is guided to the seedling planting device raising / lowering hydraulic circuit via the external pipe 97, used for the operation of the hydraulic cylinder 5 via the control valve 98, and further sent out from the control valve 98. After the supplied hydraulic oil is supplied to the charging oil passage b of the main transmission 30, the surplus oil is returned to the transmission case 9.

  As shown in FIG. 9, the surplus oil filled in the casing of the main transmission 30 is introduced into the front axle case portion 9 d on the left side of the transmission case 9 via a pipe 99 provided in the transmission case 9. After that, it is returned to the mission case 9.

  As shown in FIG. 8, a blazer plug 82 having a gas-liquid separation chamber is attached to the front upper end of the mission case 9, and an insertable / removable oil gauge 83 is attached to the upper surface of the mission case 9. .

[Other Examples]
(1) The torque generator 85 is connected to the transmission case 9 in a vertical posture, and a steering operation shaft 86 extending vertically upward from the torque generator 77 and a steering shaft (not shown) that tilts the steering handle 14 backward. It can also be carried out by interlocking connection with a universal joint (not shown).

  (2) The present invention can also be applied to a manual steering type model that does not include the torque generator 85.

Whole side view of rice transplanter Overall plan view of rice transplanter Schematic diagram of transmission system Schematic diagram of transmission system Plan view across the main part of the mission case Sectional view of part of the mission case Expanded cross section of PTO transmission mechanism Right side view of the front of the mission case Front view of the front of the mission case Hydraulic circuit diagram Plan view showing the restriction structure for the maximum steering angle of the front wheels

1 Front wheel 9 Mission case 11 Front frame
11a Contact part 12 Engine 14 Steering handle 30 Hydrostatic continuously variable transmission 36 Input shaft 37 Output shaft 77 Hydraulic pump 78 Pump drive shaft 85 Torque generator 88 Steering shaft
89 Rotating shaft
90 Sect Gear
91 Pinion gear
92 Pitman Arm

Claims (4)

Equipped with steerable front wheels to the transmission case deployed on the body front, with interlocked connecting the lower and front wheel steering shaft inserted through the bearing in the vertical direction in the transmission case, is operatively connected to the transverse engine In a steering operation structure of a working machine configured to drive a hydraulic pump that supplies working pressure oil with a pump drive shaft mounted,
The input shaft of the hydrostatic continuously variable transmission connected to the side of the transmission case is linked to the engine, the output shaft of the hydrostatic continuously variable transmission is linked to the transmission system in the transmission case, Connecting the input shaft and the pump drive shaft concentrically;
The steering shaft is arranged in an up and down direction in a tilted posture so as to be along a front wall portion of the transmission case that is inclined so that the lower side is positioned on the front side from the upper side. The pump drive shaft is inserted and supported in the transmission case in the case behind the steering shaft so that the steering shaft and the pump drive shaft are close to each other ,
A rotating shaft having a pitman arm for steering the front wheel is provided on the rear side below the steering shaft in parallel with the steering shaft, and the front end portion of the pitman arm is located behind the front end portion of the transmission case. In the transmission case, the pinion gear below the steering shaft and the sect gear of the rotating shaft are engaged with each other, the pitman arm is swung by the steering shaft, and the front wheel is A steering operation structure of a work machine configured to be steered. The steering operation structure for a working machine according to claim 1 , wherein a steering handle and the steering shaft provided above the transmission case are arranged concentrically . The steering operation structure for a working machine according to claim 1 or 2, wherein the steering shaft is driven and rotated by a torque generator . 4. The engine according to claim 1 , wherein the engine is mounted on a front frame extending forward from the transmission case, and a contact portion that regulates a maximum steering angle of the front wheel is provided on the front frame. The steering operation structure of the working machine as described in 1.

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