JP5054478B2 - Work vehicle turning control device - Google Patents

Description

The present invention is a hydraulic operation type in which the driving state of the pair of left and right traveling devices can be switched between a straight driving state and a turning driving state, and is changed by changing the supply pressure of the pressure oil to which the operating pressure to be exhibited is supplied friction type hydraulic clutch is provided for, by the computer enters the frictional type hydraulic clutch, and configured travel drive means so that the traveling speed of the rotation driving state by mutually different devices of the left and right are obtained ,
Steering command means for selecting the straight drive state and the turning drive state and changing and setting the operation pressure of the friction hydraulic clutch;
Based on the operation of the steering command means, by adjusting the opening of the oil passage pressure oil is supplied from the hydraulic source, the maximum and minimum supply pressure of the supply pressure of the pressure oil to the friction type hydraulic clutch An electromagnetic proportional valve that changes and adjusts between supply pressure and
The present invention relates to a turning control device for a work vehicle provided with an operation control means for operating the travel drive means and the electromagnetic proportional valve based on a command from the steering command means.

Such a turning control device for a work vehicle, when selecting a turning drive state by the steering command means and turning, by changing and setting the operating pressure of the friction hydraulic clutch by the steering command means, The turning state can be obtained.
In the conventional turning control device, a variable relief valve for pressure oil supplied from the hydraulic pump to the friction hydraulic clutch is provided as a supply pressure adjusting means for changing and adjusting the supply pressure to the friction hydraulic clutch. An oscillating steering lever is provided as a direction command means, and an operation control means for operating the variable relief valve based on a command from the steering command means operates the variable relief valve toward the oil passage closing side. The cam mechanism and the steering lever are connected to each other through a wire. That is, although not described in detail, the steering lever is in a straight drive state at the position where neutral is commanded, and is configured to be in a turning drive state when the steering lever is operated away from the neutral position. The relief pressure of the variable relief valve is configured to increase gradually and continuously as the direction lever is operated farther away from the neutral position (see, for example, Patent Document 1).
Incidentally, in this patent document 1, as the friction type hydraulic clutch, there are provided one that switches to a super turning state and one that switches to a slow turning state, and any friction type hydraulic clutch is provided by a switching lever as a turning state selection means. Whether to switch to the turning state using a hydraulic clutch is selected.

JP-A-8-19304

Conventionally, the relief pressure of the variable relief valve is configured to increase gradually and continuously as the steering lever is operated farther away from the neutral position. For example, even if the steering lever is operated at the stroke end, the relief pressure of the variable relief valve is not operated to the maximum value, and the inherent turning performance may not be fully utilized .

  The present invention has been made in view of the above circumstances, and its purpose is a work that can be operated so as to fully utilize the turning performance originally provided in a form that is easy for the operator to drive. The object is to provide a vehicle turning control device.

The turning control device for a work vehicle according to the present invention is capable of switching the drive state of the pair of left and right traveling devices between a straight drive state and a turn drive state, and changing the supply pressure of the pressure oil to which the operating pressure to be exhibited is supplied A hydraulically operated frictional hydraulic clutch that is changed by the above-mentioned, and by turning the frictional hydraulic clutch into the engaged state, the speed of the left and right traveling devices can be made different from each other so that the turning drive state can be obtained. Configured travel drive means;
Steering command means for selecting the straight drive state and the turning drive state and changing and setting the operation pressure of the friction hydraulic clutch;
Based on the operation of the steering command means, by adjusting the opening of the oil passage pressure oil is supplied from the hydraulic source, the maximum and minimum supply pressure of the supply pressure of the pressure oil to the friction type hydraulic clutch An electromagnetic proportional valve that changes and adjusts between supply pressure and
On the basis of the command steering command means, the operation control means for operating said travel drive means and the electromagnetic proportional valve, a work vehicle turning control device is provided,
The travel drive means includes a plurality of friction type hydraulic clutches that are switched to a plurality of types of turning drive states by selectively entering the turning drive state as the friction type hydraulic clutch,
The steering command means continuously commands a target value between the minimum target value for commanding the minimum operating pressure and the maximum target value for commanding the maximum operating pressure as information for changing the operating pressure. Composed of
The operation control means selectively puts the plurality of frictional hydraulic clutches in the turning drive state based on a command of a turning state selection means for selecting any of the plurality of types of turning drive states. Composed of
As the plurality of types of turning drive states, the target value of the steering command means is different from the target speed ratio of the left and right traveling devices when the maximum target value is commanded by the steering command means. A relationship with the target speed ratio is set ,
In any of the plurality of types of turning driving states, the target speed ratio corresponding to the turning driving state is set so as to appear when the opening of the oil passage is maximum,
The operation control means is configured such that, even if any one of the plurality of types of turning drive states is selected by the turning state selecting means, the steering command means is configured to reduce the minimum in the selected turning drive state. When a target value between a target value and a target value immediately before the maximum target value is commanded, a drive current corresponding to the target value commanded by the steering command means is applied to the electromagnetic proportional valve. supply to, the supply pressure to adjust between the minimum supply pressure and the maximum setting than the supply pressure amount small supply pressure, and the maximum target value and the target immediately before at the steering command means When a target value between values is commanded, the opening of the oil passage is maximized with respect to the electromagnetic proportional valve so that the target speed ratio corresponding to the selected turning drive state is obtained. Drive current with a predetermined amount added to the current value required for Supplies, there the supply pressure to a point that is configured to adjust the maximum supply pressure.

When one of a plurality of types of turning drive states is selected by the turning state selection means, the friction corresponding to the turning drive state selected by the turning state selection means among the plurality of friction type hydraulic clutches by the operation control means. The type hydraulic clutch is operated in the engaged state, and can turn. In other words, it is possible to perform good work while selecting different turning states depending on the field conditions and work conditions by allowing multiple types of turning driving states to appear differently. Therefore, even if the field conditions and work conditions are different, it is possible to turn in a turning drive state corresponding to the conditions.
The steering command means continuously commands the target value between the minimum target value for commanding the minimum operating pressure and the maximum target value for commanding the maximum operating pressure as information for changing the operating pressure. to become, element, when the target value between the minimum target value by steering command means to the target value of the previous maximum target value is instructed, the changes adjusts the supply pressure of the pressurized oil to the friction type hydraulic clutch The drive current corresponding to the target value commanded by the steering command means is supplied to the proportional solenoid valve, and between the minimum supply pressure in the adjustment range and the supply pressure that is smaller than the maximum supply pressure by a set amount. An electromagnetic proportional valve is operated to adjust the supply pressure . Further, when a target value between the maximum target value and the immediately preceding target value is commanded by the steering command means, an electromagnetic proportional valve is obtained so that a target speed ratio corresponding to the selected turning drive state is obtained. On the other hand, a drive current obtained by adding a predetermined amount to a current value necessary for maximizing the opening of the oil passage is supplied to adjust the supply pressure to the maximum supply pressure.
That is, when the target value between the minimum target value and the target value immediately before the maximum target value is commanded by the steering command means, the set amount is larger than the minimum supply pressure and the maximum supply pressure in the adjustment range of the electromagnetic proportional valve. Since the electromagnetic proportional valve is operated so as to adjust the supply pressure with a small supply pressure, the supply pressure of the pressure oil to the friction type hydraulic clutch changes with the change of the target value of the steering command means. When the steering command means commands a target value between the maximum target value and the target value just before it , the oil proportional valve is opened. The supply pressure is adjusted to the maximum supply pressure by supplying a drive current obtained by adding a predetermined amount to the current value necessary to maximize the pressure. As the pressure oil supply pressure can be accurately controlled to the maximum supply pressure, That.

Thus, since the one supply pressure to the friction type hydraulic clutch always changes with a change in the target value for commanding at steering command means, and at the operator is assumed easily operated, also, the command steering command means, the test Kyu圧a and than the ones can be accurately operated to maximize feed pressure, has been, to fully utilize the turning performance operator is originally provided in easily form operated It came to provide the turning control apparatus of the work vehicle which can be operated to.

The second characteristic configuration of the turning control device for a work vehicle according to the present invention is in addition to the first characteristic configuration described above,
While the target value from the minimum target value to the target value immediately before the maximum target value is commanded by the steering command unit, the target value commanded by the steering command unit and the electromagnetic proportional valve are supplied. The correlation with the drive current is a quadratic function such that the change amount of the drive current with respect to the unit change amount of the target value increases as the target value increases from the minimum target value toward the maximum target value. It is in the point set to the relationship corresponding to .

In addition to the first or second characteristic configuration, the third characteristic configuration of the turning control device for a work vehicle according to the present invention includes:
Among the oil passages, a pressure switch that is turned on when the oil pressure of the oil passage becomes a predetermined value or more is provided between the hydraulic pressure source and the electromagnetic proportional valve,
Until the predetermined time elapses after the steering command means changes from the state in which the minimum target value is instructed to the state in which the target value on the maximum target value side is instructed, the operation control means has the pressure switch turned on. Until then, the electromagnetic proportional valve is configured to supply a drive current obtained by adding a predetermined amount to a current value necessary for maximizing the opening of the oil passage .

  Hereinafter, the case where the embodiment of the turning control device for a work vehicle according to the present invention is applied to a combine as an example of the work vehicle will be described with reference to the drawings.

  As shown in FIG. 1, a cutting part 4 is supported at a front part of a vehicle body supported by right and left crawler travel devices 1 and 1 by a lifting cylinder 3 so as to be driven up and down around a horizontal axis P1. A driving unit 5 is provided on the right side of the front of the vehicle, an engine 7 (see FIG. 2) is provided below the driving seat 6 of the driving unit 5, a threshing device 8 is provided on the left side of the rear part of the vehicle body, and A Glen tank 9 is provided on the right side of the rear part to constitute a self-removing combine that is an example of a work vehicle.

  As shown in FIG. 2, the power of the engine 7 is transmitted to the hydrostatic continuously variable transmission 11 for traveling speed change via the transmission belt 19, the input pulley 17, and the input shaft 16, while the power of the engine 7 is It is configured to be transmitted to the cutting unit 4 through the transmission belt 20 and the hydrostatic continuously variable transmission 21 for cutting and shifting.

Next, the transmission mechanism inside the mission case will be described with reference to FIG.
An input shaft 22 is supported on the upper part of the transmission case 10, and transmission gears 23 and 24 are fixed to the input shaft 22 by a spline structure. An output shaft 11c of the hydrostatic continuously variable transmission 11 is inserted into the transmission case 10 and connected to the transmission gear 24 (input shaft 22) by a spline structure. Further, a high-speed gear 25 and a low-speed gear 26 are externally fitted to the sub-transmission transmission shaft 27 supported on the upper portion of the transmission case 10 so as to be relatively rotatable, and the transmission gear 23 and the high-speed gear 25, the transmission gear 24 and the low-speed gear 26 are fitted. The shift member 28 is externally fitted to the sub-transmission transmission shaft 27 so as to be integrally rotatable and slidable by a spline structure. The transmission gear 23 and the high-speed gear 25, the transmission gear 24 and the low-speed gear 26, and the shift member 28 constitute an auxiliary transmission, and the input shaft 22 is engaged by engaging the shift member 28 with the high-speed and low-speed gears 25 and 26. Is transmitted to the sub-transmission transmission shaft 27 after being shifted to high and low two stages (low speed and high speed position).
The auxiliary transmission is normally slid to a position where the shift member 28 meshes with the high speed gear 25 to set the high speed position.

A linear transmission shaft 29 is supported at the lower part of the transmission case 10, and a transmission gear 31 is fixed to the linear transmission shaft 29. The transmission gear 31 is engaged with a transmission gear 30 fixed to the auxiliary transmission transmission shaft 27. Yes. Also, a pair of left and right output gears 32R and 32L are fitted on the linear transmission shaft 29 so as to be relatively rotatable, and a pair of left and right occlusion portions 33R and 33L are integrally rotated with the linear transmission shaft 29 by a spline structure. It is slidably fitted outside. Then, the right side clutch 34 between the right output gear 32R and right engaging portion 3 3 R is formed, the left side clutch 34 is configured between the left output gear 32L and the left engaging portion 3 3 L Has been.

Next, the right and left side clutches 34 will be described.
Spline portions are formed on the outer surfaces of the right and left side portions of the straight transmission shaft 29, and the right occlusion portion 33R and the left occlusion portion 33L are externally fitted to the spline portion of the straight movement transmission shaft 29 so as to be integrally rotatable and slidable. The receiving member 40 is externally fitted to the spline portion of the linear transmission shaft 29 so as to be integrally rotatable. The right and left occlusal portions 33R and 33L are urged by the receiving member 40 and the spring 41 to the occlusal side of the right and left output gears 32R and 32L. The right and left occlusal portions 33R and 33L are engaged with the right and left output gears 32R and 32L, so that the right and left side clutches 34 are in a transmission state. And the left and right crawler travel devices 1 and 1 via the left side clutch 34.

  Further, by supplying hydraulic oil into the oil chambers formed between the right and left output gears 32R and 32L and the right and left occlusion portions 33R and 33L, the right and left occlusion portions 33R and 33L The right and left occlusal portions 33R and 33L are slid to the side where they are separated against the biasing force of the spring 41, and the right and left side clutches 34 are in a clutch disengaged state (disengaged state). When the hydraulic oil is discharged, the right and left side clutches 34 are engaged (transmission state) by the biasing force of the spring 41.

The left and right transmission shafts 35 are supported on the same axis so as to be arranged side by side on the same axis, and the left and right transmission gears 36 fixed to the left and right transmission shafts 35 are connected to the right output gear 32R and the left. of which meshed with the output gear 32L, the left and right left and right transmission gear 37 fixed to the transmission shaft 35 has meshed with the transmission gear 39 respectively fixed to the right and left axles 38. The right and left axles 38 are connected to the sprockets of the right and left crawler travel devices 1 and 1.

  If both the left and right side clutches 34 are engaged, the power of the input shaft 22 is transmitted to the sub-transmission transmission shaft 27, the transmission gears 30 and 31, the straight transmission shaft 29, the right and left side clutches 34, When transmitted to the right and left crawler travel devices 1 and 1 via the right and left output gears 32R and 32L, the transmission gear 36, the transmission shaft 35, the transmission gears 37 and 39, and the right and left axles 38, the machine body Becomes a transmission state in which the vehicle travels straight.

Next, the structure of the turning transmission system for turning the vehicle body will be described.
A transmission shaft 44 is supported in the transmission case 10, and a transmission gear 45 fitted on the transmission shaft 44 so as to be relatively rotatable is engaged with a gear portion on the outer periphery of the right occlusion portion 33 </ b> R. A slow turning clutch 46 is provided between the gear 45. The slow swing clutch 46 is configured as a friction multi-plate type, and is operated to a transmission state (on state) when hydraulic oil is supplied, and is operated to a cut-off state (off state) when the hydraulic oil is discharged. .

  A revolving clutch case 47 is fitted on the linear transmission shaft 29 so as to be relatively rotatable, and a transmission gear 48 fixed to the transmission shaft 44 and a transmission gear 47 a on the outer periphery of the revolving clutch case 47 are engaged with each other. The turning clutch case 47 is configured to be bilaterally symmetrical, and a right and left turning clutch 49 is formed between the turning clutch case 47 and the right and left output gears 32R and 32L. The right and left turning clutch 49 is configured as a friction multi-plate type, and is operated in a transmission state by supplying hydraulic oil. The right and left turning clutches 49 are arranged so that the friction plates are dense with each other, and the right and left turning clutches 49 are in a semi-transmission state even when the hydraulic oil is discharged. .

  When the slow swing clutch 46 is operated in the transmission state, the power of the straight drive shaft 29 is used for the straight drive via the right occlusal portion 33R, the transmission gear 45, the slow swing clutch 46, the transmission shaft 44, and the transmission gear 48. Rotation in the same direction as the transmission shaft 29 is transmitted to the turning clutch case 47 as power lower than that of the linear transmission shaft 29. When one of the right and left side clutches 34 is operated in a disconnected state and the one of the right or left turning clutch 49 on the side where the side clutch 34 is disconnected is operated in a transmission state, a transmission state is established. Through the turning clutch 49, the power in the same direction as that of the straight transmission shaft 29 is transmitted to one of the right and left output gears 32R and 32L by the rotation in the same direction as that of the straight transmission shaft 29. Low speed power is transmitted to the traveling device 1. At that time, the power of the straight drive shaft 29 is transmitted as it is to the other of the right or left output gears 32R, 32L.

  The transmission shaft 44 is provided with a frictional multi-plate hydraulic brake 50. The hydraulic brake 50 is operated in a braking state (on state) when hydraulic oil is supplied, and the hydraulic oil is discharged. The brake is released (disengaged). When the hydraulic brake 50 is operated to a braking state, the turning clutch case 47 is brought into a braking state via the transmission shaft 44 and the transmission gear 48. When one of the right and left side clutches 34 is operated to the disconnected state, and the one of the right or left turning clutch 49 on the side where the side clutch 34 is disconnected is operated to the transmission state, the right or left side clutch 34 is operated. Of the output gears 32R and 32L, the side where the side clutch 34 is not disengaged is in a braking state, and the power on the opposite side transmits the power of the straight transmission shaft 29 as it is.

Further, the transmission shaft 44, transmission gear 52 is fitted to rotate relative, the transmission gear 52, transmission gear 51 provided on rotatable together the sub speed-change driving shaft 27 is meshed. A reverse clutch 53 is provided between the transmission shaft 44 and the transmission gear 52. The reverse clutch 53 is configured as a frictional multi-plate type, and is operated to a transmission state (on state) when hydraulic oil is supplied, and is operated to a cut-off state (off state) when the hydraulic oil is discharged.

  When the reverse clutch 53 is operated in the transmission state, the power of the sub-transmission transmission shaft 27 is reverse to the linear transmission shaft 29 via the transmission gears 51 and 52, the reverse clutch 53, the transmission shaft 44 and the transmission gear 48. It is transmitted to the turning clutch case 47 as directional rotation power. When one of the right and left side clutches 34 is operated in a disconnected state and the one of the right or left turning clutch 49 on the side where the side clutch 34 is disconnected is operated in a transmission state, a transmission state is established. The rotational power in the direction opposite to that of the straight transmission shaft 29 is transmitted to one of the right or left output gears 32R and 32L via the turning clutch 49, and the reverse rotation is transmitted to the traveling device 1 on the corresponding side. Power is transmitted. At that time, the power of the straight drive shaft 29 is transmitted as it is to the other of the right or left output gears 32R, 32L.

Accordingly, each of the slow swing clutch 46, the hydraulic brake 50, and the reverse clutch 53 corresponds to a plurality of hydraulically operated frictional hydraulic clutches M. A transmission mechanism provided in the above-described transmission case 10 including the left and right side clutches 34 for switching the driving state of the traveling device between the straight drive state and the turning drive state as a main component is a pair of left and right traveling devices. 1 can be switched between a straight drive state and a swing drive state, and a plurality of swing drive can be performed by selectively turning on a plurality of hydraulically operated frictional hydraulic clutches M in the swing drive state. It corresponds to the traveling drive means 100 configured to switch to a state.
Incidentally, in each of the plurality of friction hydraulic clutches M, the diameter, the number of friction plates , and the spring constant of the return spring are set so as to increase the variable range of the transmission torque with respect to the input pressure as will be described later. Become.

Next, the operation of the hydrostatic continuously variable transmission 11 for traveling speed change will be described with reference to FIG.
The pump 11P of the hydrostatic continuously variable transmission 11 is configured to be continuously variable from the neutral position N and the neutral position N to the high speed side of the forward F and the high speed side of the reverse R. The hydrostatic continuously variable transmission Eleven motors 11M are configured to be variable in two levels. A hydraulic cylinder 59 for operating the swash plate of the pump 11P of the hydrostatic continuously variable transmission 11 and a control valve 60 for supplying / discharging hydraulic oil to / from the hydraulic cylinder 59 are provided, and a shift lever 61 provided in the operating unit 5 is provided. And the control valve 60 are mechanically linked. Thus, by operating the speed change lever 61, the control valve 60 is operated and the hydraulic cylinder 59 is operated, and the pump 11P of the hydrostatic continuously variable transmission 11 is tilted to a position corresponding to the operation position of the speed change lever 61. Operate the board.

  A hydraulic cylinder 62 that operates the swash plate of the motor 11M of the hydrostatic continuously variable transmission 11 and an electromagnetically operated control valve 63 that supplies and discharges hydraulic oil to and from the hydraulic cylinder 62 are provided. A shift switch 61a is provided in the unit, and an operation signal of the shift switch 61a of the shift lever 61 is input to a control device 64 including a microcomputer. Thus, by operating the speed change switch 61a of the speed change lever 61, the control valve 63 is operated by the control device 64, the hydraulic cylinder 62 is operated, and the swash plate of the motor 11M of the hydrostatic continuously variable transmission 11 is operated at high speed. And it is the structure operated to a low-speed position.

  An operation position sensor 65 for detecting the operation position of the shift lever 61 is provided, and left and right axle rotation sensors 66R and 66L for detecting the rotation speeds of the left and right axles for detecting the traveling speed of the airframe are provided. Detection values of the position sensor 65 and the left and right axle rotation sensors 66R and 66L are input to the control device 64. Detection of whether the swash plate of the motor 11M of the hydrostatic continuously variable transmission 11 is at the high speed position or the low speed position is recognized by the control device 64 based on the operation signal of the speed change switch 61a of the speed change lever 61. As a result, the subtransmission (shift member 28) is determined based on the operating position of the pump 11P and the motor 11M of the hydrostatic continuously variable transmission 11 and the traveling speed of the airframe determined from the average value of the detected values of the left and right axle rotation sensors 66R and 66L. Can be recognized as a high speed position or a low speed position.

Next, hydraulic oil is supplied to and discharged from the right and left side clutches 34 (right and left occlusal portions 33R and 33L), right and left turning clutch 49, slow turning clutch 46, hydraulic brake 50, and reverse clutch 53. The hydraulic unit 57 will be described.
As shown in FIG. 4, the hydraulic unit 57 includes a right turn control valve 67, a left turn control valve 68, a relief valve 69, an unload valve 70, a proportional control valve 71, a turn switching control valve 72, a belief turn. Pilot valve 73 and super-revolution pilot valve 74 are provided. The external pipe 58 from the hydraulic pump 56 driven by the output shaft 11 b of the hydrostatic continuously variable transmission 11 is connected to the hydraulic unit 57, and the right turning control valve 67 is an oil path 29 b of the straight transmission shaft 29. Are connected to the right side clutch 34 and the right turning clutch 49, and the left turning control valve 68 is connected to the left side clutch 34 and the left turning clutch 49 via the oil passage 29b of the straight transmission shaft 29. ing.

  The right turn control valve 67 and the left turn control valve 68 are configured by electromagnetic operation that can be switched to two positions of supply positions 67a and 68a and discharge positions 67b and 68b, respectively. The return is energized. The unload valve 70 is configured in an electromagnetic operation type that can be switched between two positions of a blocking position 70a and a discharging position 70b, and is urged to return to the blocking position 70a. A proportional control valve 71 and a turning switching control valve 72 are connected in series to an oil passage 75 branched from between the right and left turning control valves 67 and 68 and the oil passage 29b of the transmission shaft 29 for straight travel. The switching control valve 72 is connected to the slow turning clutch 46 and the reverse rotation clutch 53 via the oil passage 44 a of the transmission shaft 44, and the turning switching control valve 72 is connected to the hydraulic brake 50 via the oil passage 76 of the hydraulic unit 57. Yes.

  The proportional control valve 71 is composed of an electromagnetic proportional valve, and changes and adjusts the control current supplied from the control device 64 as will be described later, whereby the friction type hydraulic clutches M (relaxation) on the lower side of the hydraulic fluid flow path are controlled. The supply pressure to the swing clutch 46, the hydraulic brake 50, and the reverse clutch 53) can be changed and adjusted. Accordingly, the proportional control valve 71 constitutes a supply pressure adjusting means for changing and adjusting the supply pressure of the pressure oil supplied from the hydraulic source to the friction hydraulic clutch M.

  The turning switching control valve 72 is configured as a pilot operated type that can be operated to a slow turning position 72a, a trust turning position 72b, and a super turning position 72c, and is urged to return to the slow turning position 72a. A pilot turning pilot valve 73 is configured so that pilot hydraulic oil branched from the oil passage 75 is supplied to the turning switching control valve 72 and operated to the trust turning position 72b, and the pilot hydraulic oil branched from the oil passage 75 is supplied. A super pivot pilot valve 74 is configured to be supplied to the pivot switching control valve 72 and operated to the super pivot position 72c. The pivot switch pilot valve 73 and the super pivot pilot valve 74 each stop the supply position for supplying pilot hydraulic oil to the swing switching control valve 72 and the supply of pilot hydraulic oil, and the swing switching control valve. It is configured as an electromagnetic operation type that can be switched to two positions of a stop position for returning 72 to neutral, and is urged to return to the stop position.

  The right turn control valve 67, the left turn control valve 68, the unload valve 70, the proportional control valve 71, the pivot pilot valve 73, and the super pivot pilot valve 74 are controlled by a control device 64 as described later. Controlled.

  Then, as shown in FIG. 5, the return command is urged to return to the straight command position N, and the turn command operation region extends from the straight command position N to the maximum operation position Rm on the right side and the maximum operation position Lm on the left side. A swing lever 77 capable of swinging operation is provided in the operation unit 5, and a swing lever sensor 80 is provided as a turn command position detecting means for detecting an operation position of the swing lever 77. It is input to the control device 64.

  The swivel lever 77 can be freely moved over the straight command position N and the swivel command operation area connected thereto, and the swivel lever sensor 80 has a maximum operation position (Rm, The detection information corresponding to the target turning force that increases as the movement to Lm) is commanded to the control device 64, and the steering command means 200 is constituted by the turning lever 77 and the turning lever sensor 80.

In addition, a turning mode switch 78 for instructing to switch the turning driving state to a slow turning state, a trust turning state, and a super turning state is provided in the operation unit 5, and the operation position of the turning mode switch 78 is controlled by the control device 64. This turning mode switch 78 is operated to switch between a slow turning position corresponding to the gentle turning state, a trust turning position corresponding to the trust turning state, and a super faith turning position corresponding to the super trust turning state. A frictional hydraulic clutch that is configured freely and that corresponds to a turning mode selected from the slow turning clutch 46, the hydraulic brake 50, and the reverse rotation clutch 53 according to the operation position of the turning mode switch 78. By turning M into the on state, the turning drive state of the travel drive means 100 is switched.

Accordingly, the turning mode switch 78 constitutes a turning state selection means for selecting one of a plurality of kinds of turning driving states, and the control device 64 constitutes an operation control means.

  When the turning lever 77 is operated to the rectilinear command position N, the right and left turning control valves 67 and 68 are operated to the discharge positions 67b and 68b, the unload valve 70 is operated to the discharge position 70b, and the right and left The hydraulic oil is discharged from the side clutch 34 and the right and left turning clutch 49, the right and left side clutch 34 are operated to the transmission state, and the right and left turning clutch 49 are operated to the half transmission state. Since the right and left turning control valves 67 and 68 are operated to the discharge positions 67b and 68b and the unload valve 70 is operated to the discharge position 70b, the hydraulic oil from the hydraulic pump 56 passes to the transmission case 10 through the unload valve 70. Returned.

  As a result, the power of the input shaft 22 is transmitted to the sub-transmission transmission shaft 27, the transmission gears 30, 31, the linear transmission transmission shaft 29, the right and left side clutches 34 (the right and left occlusion portions 33R, 33L), the right and The aircraft is transmitted straight to the right and left crawler travel devices 1 via the left output gears 32R and 32L, the transmission gear 36, the transmission shaft 35, the transmission gears 37 and 39, and the right and left axles 38.

Next, the case where the turning lever 77 is operated to the turning command operation area when the turning mode switch 78 is operated to the slow turning position will be described.
When the turning mode switch 78 is operated to the slow turning position and the turning lever 77 is operated to the right from the straight command position N to move out of the dead zone, the right turning control valve 67 is operated to the supply position 67a to unload. The valve 70 is switched to the shut-off position 70a, hydraulic oil is supplied to the right side clutch 34 (right occlusion portion 33R) and the right turning clutch 49, and the right side clutch 34 (right occlusion portion 33R) is shut off. The hydraulic oil is supplied to the right turning clutch 49 and is operated to the transmission state.

  In this case, since the left turning clutch 49 is in a semi-transmission state, the power of the left side clutch 34 is transmitted from the left output gear 32L and the left turning clutch 49 to the right output gear 32R via the right turning clutch 49. The power slightly lower than that of the linear transmission shaft 29 is transmitted to the right output gear 32R by rotation in the same direction as the linear transmission shaft 29. As a result, the aircraft gently turns to the right.

  When the swivel lever 77 is operated rightward from the rectilinear command position N and moves out of the dead zone, the proportional control valve 71 and swivel switching are almost simultaneously with the right swivel control valve 67 being operated to the supply position 67a as described above. The hydraulic oil begins to be supplied to the slow swing clutch 46 via the control valve 72, and as the swing lever 77 is moved to the right in a direction away from the straight advance command position after moving out of the dead zone, the proportional control valve 71 becomes slower. The operation pressure of the swing clutch 46 is increased.

  As the operation pressure of the slow swing clutch 46 is increased by the proportional control valve 71 based on the operation position of the swing lever 77, the power of the straight transmission shaft 29 is changed to the right occlusal portion 32R, the transmission gear 45, Through the turning clutch 46, the transmission shaft 44, the transmission gear 48, the turning clutch case 47 and the right turning clutch 49, the motive power at a lower speed than the straight traveling transmission shaft 29 is rotated in the same direction as the straight traveling transmission shaft 29. It is transmitted to the output gear 32R.

  In this case, the power from the left side clutch 34 (the left occlusal portion 33L) and the power from the slow turning clutch 46 are transmitted to the right output gear 32R at the same time. In the range where the operation pressure is low, the power from the left side clutch 34 (the left occlusion portion 33L) overcomes the power from the slow swing clutch 46, and the power from the left side clutch 34 (the left occlusion portion 33L). As a result, the right output gear 32R is driven. As a result, when the operating pressure of the gentle turning clutch 46 is low, the aircraft gradually turns to the right.

  When the amount of movement of the turning lever 77 to the right increases and the operating pressure of the slow turning clutch 46 increases, the power from the slow turning clutch 46 overcomes the power from the left side clutch 34 (left occlusal portion 33L). Thus, the right output gear 32R is driven by the power from the slow turning clutch 46. In this state, the right output gear is driven by the power from the slow turning clutch 46 rather than the left output gear 32L driven by the power of the straight transmission shaft 29 via the left side clutch 34 (the left engagement portion 33L). 32R will be driven at low speed and the aircraft will turn slowly to the right.

  When the swivel lever 77 is operated to the left from the rectilinear command position N and moves out of the dead zone, the left swivel control valve 68 is operated to the supply position 68a, the unload valve 70 is held at the shut-off position 70a, and the left side The hydraulic oil is supplied to the clutch 34 (the left occlusion portion 33L) and the left turning clutch 49, the left side clutch 34 (the left occlusion portion 33L) is operated to be disconnected, and the left turning clutch 49 is operated with the hydraulic oil. Is operated in the transmission state. At the same time, the same operation as the left turn described above is performed, and the aircraft gradually turns to the left. Further, when the operation amount to the right side of the turning lever 77 increases and the operation pressure of the slow turning clutch 46 becomes high, the same operation as the right turning operation is performed, and the aircraft turns slowly to the left.

Next, the case where the turning lever 77 is operated to the turning command operation area when the turning mode switch 78 is operated to the conviction turning position will be described.
When the turning mode switch 78 is operated to the cruciform turning position and the turning lever 77 is operated rightward from the rectilinear command position N to move out of the dead zone, the right turning control valve 67 is operated to the supply position 67a to unload. The valve 70 is switched to the shut-off position 70a, hydraulic oil is supplied to the right side clutch 34 (right occlusion portion 33R) and the right turning clutch 49, and the right side clutch 34 (right occlusion portion 33R) is shut off. The hydraulic oil is operated to the right turning clutch 49 in the transmission state. In this case, since the left turning clutch 49 is in a semi-transmission state, the aircraft gradually turns to the right.

  When the swivel lever 77 is operated rightward from the rectilinear command position N and moves out of the dead zone, the proportional control valve 71 and swivel switching are almost simultaneously with the right swivel control valve 67 being operated to the supply position 67a as described above. The hydraulic oil begins to be supplied to the hydraulic brake 50 via the control valve 72 (the pivot position 72b), and the pivot lever 77 is moved to the right in the direction away from the dead reckoning command position after leaving the dead zone. The operation pressure of the hydraulic brake 50 is increased by the proportional control valve 71.

  As the operation pressure of the hydraulic brake 50 is increased by the proportional control valve 71 in accordance with the operation of the turning lever 77, the transmission shaft 44, the transmission gear 48, the turning clutch case 47, and the right turning clutch 49 are used. A braking force is applied to the right output gear 32R.

  In this case, since the power from the left side clutch 34 (the left occlusal portion 33L) and the braking force of the hydraulic brake 50 are transmitted to the right output gear 32R at the same time, the operating pressure of the hydraulic brake 50 is increased. In the low pressure range, the power from the left side clutch 34 (left occlusion portion 33L) overcomes the braking force of the hydraulic brake 50, and the power from the left side clutch 34 (left occlusion portion 33L) The output gear 32R is driven. As a result, when the operating pressure of the hydraulic brake 50 is low, the aircraft gradually turns to the right.

  When the amount of movement of the swivel lever 77 to the right increases and the operating pressure of the hydraulic brake 50 becomes high, the braking force of the hydraulic brake 50 overcomes the power from the left side clutch 34 (left occlusal portion 33L). The right output gear 32R enters the braking state by the braking force of the hydraulic brake 50, and the aircraft turns right.

  When the turning lever 77 is operated to the left from the rectilinear command position N to move out of the dead zone, the left turning control valve 68 is operated to the supply position 68a, the unload valve 70 is operated to the cutoff position 70a, and the left side clutch 34 (the left occlusion portion 33L) and the left turning clutch 49 are supplied with hydraulic oil, the left side clutch 34 (the left occlusion portion 33L) is operated to be disconnected, and the left turning clutch 49 is supplied with hydraulic oil. Operated in transmission state. At the same time, the same operation as described above is performed, and the aircraft gradually turns to the left. When the amount of movement of the turning lever 77 to the left increases and the operating pressure of the hydraulic brake 50 becomes high, the same operation as the right turning operation is performed, and the aircraft turns to the left.

Next, the case where the turning lever 77 is operated to the turning command operation area when the turning mode switch 78 is operated to the super turning position will be described.
When the turning mode switch 78 is operated to the super turning position, and the turning lever 77 is operated rightward from the straight travel command position N to move out of the dead zone, the right turning control valve 67 is operated to the supply position 67a and The load valve 70 is switched to the shut-off position 70a, hydraulic oil is supplied to the right side clutch 34 (right occlusion portion 33R) and the right turning clutch 49, and the right side clutch 34 (right occlusion portion 33R) is moved. The shut-off state is operated, and the right turning clutch 49 is operated in the transmission state. In this case, since the left turning clutch 49 is in a semi-transmission state, the aircraft gradually turns to the right.

  When the swivel lever 77 is operated rightward from the rectilinear command position N and moves out of the dead zone, the proportional control valve 71 and swivel switching are almost simultaneously with the right swivel control valve 67 being operated to the supply position 67a as described above. The hydraulic oil starts to be supplied to the reverse rotation clutch 53 via the control valve 72 (super pivot turning position 72c), and the proportional control valve is moved as the turning lever 77 moves to the right side out of the dead zone from the straight advance command position. 71 increases the operating pressure of the reverse clutch 53.

  As the operation pressure of the reverse clutch 53 is increased by the proportional control valve 71 in accordance with the operation of the turning lever 77, the power of the subtransmission transmission shaft 27 is transmitted to the transmission gears 51, 52, the reverse clutch 53, the transmission shaft. 44, the transmission gear 48, the turning clutch case 47, and the right turning clutch 49 are transmitted to the right output gear 32R as the rotational power in the direction opposite to that of the straight drive shaft 29.

  In this case, since the power from the left side clutch 34 (the left occlusal portion 33L) and the power from the reverse clutch 53 are simultaneously transmitted to the right output gear 32R, the operation pressure of the reverse clutch 53 is reached. In the low pressure range, the power from the left side clutch 34 (the left occlusion portion 33L) overcomes the power from the reverse clutch 53, and the power from the left side clutch 34 (the left occlusion portion 33L) The output gear 32R is driven. As a result, when the operating pressure of the reverse clutch 53 is in a low pressure range, the aircraft gradually turns to the right.

  Then, when the amount of movement of the turning lever 77 to the right increases and the operating pressure of the reverse clutch 53 becomes high, the power from the reverse clutch 53 becomes the power from the left side clutch 34 (the left occlusal portion 33L). The right output gear 32R is driven by the power from the reverse clutch 53 by overcoming it. In this state, the right output gear 32R is driven in the opposite direction with respect to the left output gear 32L, and the aircraft turns to the right.

  Next, when the turning lever 77 is operated leftward from the rectilinear command position N, when the dead zone is removed, the left turning control valve 68 is operated to the supply position 68a, and the unload valve 70 is moved to the cutoff position 70a. The hydraulic oil is supplied to the left side clutch 34 (left occlusion portion 33L) and the left turning clutch 49, and the left side clutch 34 (left occlusion portion 33L) is operated to be disconnected, The hydraulic oil is operated in the transmission state to the swing clutch 49. At the same time, the same operation as described above is performed, and the aircraft gradually turns to the left. When the amount of operation for moving the turning lever 77 to the left increases and the operating pressure of the reverse clutch 53 becomes high, the same operation as in the case of right turning is performed, and the aircraft turns to the left.

By the way, when the turning mode switch 78 is operated to the slow turning position and turning in the slow turning mode, or the turning mode switch 78 is operated to the trust turning position, the turning in the trust turning state is performed. When performing, in the turning drive state in which the turning lever 77 is operated rightward or leftward beyond the dead zone, it may be necessary to turn with a slightly smaller radius.

  Therefore, in this combine, as shown in FIG. 5, a turning state changeover switch 81 is provided at the grip portion of the turning lever 77. For example, in the slow turning mode, when the turning state changeover switch 81 is pushed while the turning lever 77 is operated to turn, the turning switching control valve 72 is changed from the slow turning position 72a to the trust turning position 72b. When operated, the aircraft can switch to a right or left turn. This belief turning state is only while the turning state changeover switch 81 of the turning lever 77 is pushed and operated. When the turning state release switch 81 of the turning lever 77 is released and returned, the turning changeover control valve 72 is turned on. The fuselage is operated from the pivot turn position 72b to the slow turn position 72a, and the aircraft returns to the slow turn state.

Further, in the case of the pivoting state, if the turning state changeover switch 81 of the turning lever 77 is pushed and operated while the turning lever 77 is operated to turn, the turning switching control valve 72 is moved to the trust turning position 72b. , The aircraft turns to the left or right to turn to the right or left. This super-revolution turning state is only while the turning state changeover switch 81 of the turning lever 77 is being pushed. When the return operation is performed by releasing the turning state changeover switch 81 of the turning lever 77, the turning changeover control valve 72 is operated. There is operated to pivot turn position 72b from the ultra-pivot turn position 72c, the aircraft returns to the pivot turn state.

  Therefore, in this embodiment, the turning mode switch 78 and the turning state changeover switch 81 correspond to the turning state selection means.

Next, the contents of control by the control device 64 will be described.
In the state where the turning driving state is selected by the steering command means 200 and the operation pressure larger than the preset set operation pressure is instructed, the control device 64 sets another turning state by the turning state selection means. When selected, it is changed so that the operating pressure is lower than the operating pressure commanded at that time, and then the friction type hydraulic clutch M is switched to the disengaged state and corresponds to the other turning drive state. The frictional hydraulic clutch M is switched to the engaged state, and then the proportional control valve is controlled so that the operating pressure of the frictional hydraulic clutch M becomes the operating pressure commanded by the steering command means 200. It is configured.

  Further, the control device 64 moves the relationship between the operation position and the target operation pressure in the turning command operation area of the turning lever 77 constituting the steering command means 200 in a direction away from the straight command position in the turning command operation area. The unit amount of the operation position of the turning lever 77 increases as the amount increases, and as the amount of movement in the direction away from the rectilinear command position in the turning command operation region increases over the entire range of the turning command operation region. A direction corresponding to a quadratic function that changes the amount of change in the target operation pressure with respect to a change to the large side, and a direction away from the straight command position in the turning command operation region defined as a relationship corresponding to the quadratic function Corresponding to the operation position of the turning lever 77 based on the relationship between the amount of movement to the target and the target operating pressure and the operation position of the turning lever 77. Seeking a target operating pressure, and is configured to control the proportional control valve so that the target operating pressures.

For example, as shown in FIG. 6, in the slow turning state as the three types of turning driving states, when the turning lever 77 is operated to the maximum operation position, the traveling device inside the turning of the pair of left and right traveling devices. The target turning state in which the output rotational speed of the vehicle is decelerated to about 1/3 of the output rotational speed of the opposite traveling device is set (see line L1 in FIG. 6). The target speed ratio is set so that the output rotational speed of the traveling device becomes zero (see line L2 in FIG. 6), and in the superconducting turning state, the output rotational speed of the traveling device on the inner side of the turning is that of the opposite traveling device. A target speed ratio is set such that the speed is approximately 1/3 of the output rotational speed of the traveling device opposite to the driving rotational direction (see line L3 in FIG. 6).

Then, for example, as shown in FIG. 7, the operation position of the turning lever 77 and the target operation pressure (specifically, the frictional hydraulic clutch M) are adjusted so as to obtain the target speed ratio as described above through experiments and the like in advance. The target current supplied to the proportional control valve 71 that changes and adjusts the opening degree of the oil passage that supplies pressure oil to the hydraulic hydraulic clutch M). It is determined as a relationship (line L4) corresponding to a quadratic function that changes the amount of change in the target operating pressure to the large side, and is stored in the control device 64.
The line L4 is determined as described below so that the proportional control valve 71 can be accurately operated.
That is, the steering command means 200 uses the target value between the minimum target value for instructing the minimum operating pressure and the maximum target value for instructing the maximum operating pressure as information for changing the operating pressure of the frictional hydraulic clutch M. Are continuously commanded. When the steering command means 200 instructs the target value between the minimum target value and the target value immediately before the maximum target value, the control device 64 determines the minimum supply pressure in the adjustment range of the proportional control valve 71. Supply pressure larger than the maximum supply pressure of the proportional control valve 71 when the supply pressure is adjusted with a supply pressure smaller than the maximum supply pressure and when the maximum target value is commanded by the steering command means 200 The proportional control valve 71 is operated so as to adjust to the pressure.
Specifically, as shown in FIG. 7, specifically, the control device 64 uses the target value (that is, the turn) commanded by the steering command means 200 as the drive current (that is, the target current) of the proportional control valve 71. When the operation position of the lever 77 is between the minimum target value and the target value immediately before the maximum target value, the drive current is smaller than the drive current predicted to be able to open the proportional control valve 71 to the maximum. When the target value between the maximum target value and the immediately preceding target value is commanded by the steering command means 200, the drive current ( predicted that the proportional control valve 71 can be opened to the maximum The drive current (maximum current) is adjusted by adding the set surplus current B (predetermined amount) to the ( current value) .

  Further, as shown in FIG. 4, a pressure switch 82 that is turned on when the hydraulic oil pressure in the upper oil passage in the hydraulic oil flow direction of the proportional control valve 71 is equal to or higher than a set pressure is provided. Whether or not the hydraulic oil is filled in the friction hydraulic clutch M to which the hydraulic oil is supplied is detected.

Referring to the flowchart shown in FIGS. 8 and 9, it will be described the turning control of the control unit 64.
If the turning lever 77 is in the dead zone of the rectilinear command position N, it switches the unloading valve 70 to a discharge position 70 b (step 1). Further, both the left turn control valve 68 and the right turn control valve 67 are kept in the shut-off state (steps 3 and 4). When the turning lever 77 deviates from the dead zone from the straight travel command position N, the left turn control valve 68 is switched to the supply position 68a if the operation direction is the left direction, and the right turn control valve 67 is turned if the operation direction is the right direction. Switching to the supply position 67a (steps 5, 6, 7), the unload valve 70 is switched to the shut-off position 70a (step 8).

  If the gentle turning mode is set by the turning mode switch 78, the process proceeds to step 12 as it is. If the turning mode switch 78 is set to the trust turning mode, the trust turning pilot valve 73 is switched to the supply position. If the super turning mode is set by the turning mode switch 78, the super turning pilot valve 74 is switched to the supply position, and the process proceeds to step 12 (steps 10 and 11).

Then, if the set time (for example, several tens of msec) has not elapsed since the turning lever 77 is operated so as to be out of the dead zone, that is, immediately after the turning operation is started, the operation of the proportional control valve 71 is performed. Until the pressure switch 82 provided in the upper oil passage in the oil flow direction is turned on, the maximum current is supplied to the proportional control valve 71 and the hydraulic oil is supplied at the maximum opening degree (steps 12, 13, and 14). . In this manner, the hydraulic oil is quickly filled into the oil chamber of the friction type hydraulic clutch M (selected one of the slow swing clutch 46, the hydraulic brake 50, and the reverse clutch 53) so that the desired swing drive state is achieved as soon as possible. Can be made.

After the pressure switch 82 is turned on, the target current for the proportional control valve 71 is obtained by calculation based on the correlation shown in FIG. 7 corresponding to the turning mode at that time and the detection information of the turning lever sensor 80, If the swing lever 77 is not operated in the vicinity of the maximum operation position (Rm, Lm), that is, if it is not operated to a position for commanding a target value between the maximum target value and the target value immediately before it, the proportional control valve A proportional valve operation process for supplying a target current to 71 is executed (steps 15, 16, and 17). If the turning lever 77 is operated in the vicinity of the maximum operation position (Rm, Lm), that is, if it is operated to a position for commanding a target value between the maximum target value and the target value immediately before it, it is proportional. The control current is adjusted to the drive current (maximum current) obtained by adding the set surplus current B (predetermined amount) to the drive current predicted to be able to open the control valve 71 to the maximum (step 18).

[Another embodiment]
Hereinafter, other embodiments are listed.

(1) In the above embodiment, the plurality of frictional hydraulic clutches M include the slow turning clutch 46, the hydraulic brake 50, and the reverse rotation clutch 53, and the plurality of turning driving states include the slow turning state and the belief turning state. has been described by way of freely configuration switching to each of the super pivot turn state is not limited to such a configuration, even one that configured to include only any two of the turning drive state of those three rotation driving state Good. Further, it may be one comprising a separate turning drive state other than the three pivot drive state.

(2) In the above embodiment, a control device using a microcomputer is exemplified as the operation control means 64, but a mechanical servo mechanism such as a hydraulic type may be used, and a specific configuration of the operation control means 64 Can be changed in various ways.

(3) In the above embodiment, the turning state changeover switch 81 is provided as a turning state selection means in a state where a finger can be operated on the grip portion of the turning lever 77. However, such a turning state changeover switch 81 is provided. There may be no configuration.

(4) In the above-described embodiment, the steering command means 200 includes the turning lever 77 that can be freely moved over the straight command position and the turn command operation area. However, for example, a rotary operation dial or a plurality of push operations are provided. The present invention can be implemented in various forms such as a configuration including a type switch.

(5) In the above embodiment, the combine is shown as the work vehicle. However, the present invention can also be applied to agricultural work vehicles other than the combine vehicle and other work vehicles.

Overall side view Diagram showing transmission structure Diagram showing travel drive means Hydraulic circuit diagram Control block diagram The figure which shows the correlation between the turning lever operation position and the target speed ratio A diagram showing the correlation between the swiveling lever operation position and the target current Flow chart of control operation Flow chart of control operation

DESCRIPTION OF SYMBOLS 1,1 Traveling apparatus 46 Friction type hydraulic clutch 50 Friction type hydraulic clutch 53 Friction type hydraulic clutch 64 Operation control means 71 Electromagnetic proportional valve 77 Turning lever 78, 81 Turning state selection means
82 Pressure switch 100 Travel drive means 200 Steering command means M Friction hydraulic clutch

Claims (3)

Hydraulically operated frictional hydraulic pressure that can be switched between a straight drive state and a turning drive state between the pair of left and right traveling devices and that is changed by changing the supply pressure of the pressure oil to which the operating pressure to be exerted is supplied A travel drive means configured to be provided with a clutch and configured to obtain the turning drive state by changing the speed of the left and right travel devices from each other by putting the friction hydraulic clutch into an engaged state;
Steering command means for selecting the straight drive state and the turning drive state and changing and setting the operation pressure of the friction hydraulic clutch;
Based on the operation of the steering command means, by adjusting the opening of the oil passage pressure oil is supplied from the hydraulic source, the maximum and minimum supply pressure of the supply pressure of the pressure oil to the friction type hydraulic clutch An electromagnetic proportional valve that changes and adjusts between supply pressure and
On the basis of the command steering command means, the operation control means for operating said travel drive means and the electromagnetic proportional valve, a work vehicle turning control device is provided,
The travel drive means includes a plurality of friction type hydraulic clutches that are switched to a plurality of types of turning drive states by selectively entering the turning drive state as the friction type hydraulic clutch,
The steering command means continuously commands a target value between the minimum target value for commanding the minimum operating pressure and the maximum target value for commanding the maximum operating pressure as information for changing the operating pressure. Composed of
The operation control means selectively puts the plurality of frictional hydraulic clutches in the turning drive state based on a command of a turning state selection means for selecting any of the plurality of types of turning drive states. Composed of
As the plurality of types of turning drive states, the target value of the steering command means is different from the target speed ratio of the left and right traveling devices when the maximum target value is commanded by the steering command means. A relationship with the target speed ratio is set ,
In any of the plurality of types of turning driving states, the target speed ratio corresponding to the turning driving state is set so as to appear when the opening of the oil passage is maximum,
The operation control means is configured such that, even if any one of the plurality of types of turning drive states is selected by the turning state selecting means, the steering command means is configured to reduce the minimum in the selected turning drive state. When a target value between a target value and a target value immediately before the maximum target value is commanded, a drive current corresponding to the target value commanded by the steering command means is applied to the electromagnetic proportional valve. supply to, the supply pressure to adjust between said minimum supply pressure and the maximum setting than the supply pressure amount small supply pressure, and the maximum target value and the target immediately before at the steering command means When a target value between values is commanded, the opening of the oil passage is maximized with respect to the electromagnetic proportional valve so that the target speed ratio corresponding to the selected turning drive state is obtained. Drive current with a predetermined amount added to the current value required for By supplying, said supply pressure wheel work being configured to adjust the maximum supply pressure turn control system.   While the target value from the minimum target value to the target value immediately before the maximum target value is commanded by the steering command unit, the target value commanded by the steering command unit and the electromagnetic proportional valve are supplied. The correlation with the drive current is a quadratic function such that the change amount of the drive current with respect to the unit change amount of the target value increases as the target value increases from the minimum target value toward the maximum target value. The work vehicle turning control device according to claim 1, wherein the turning control device is set to have a relationship corresponding to. Among the oil passages, a pressure switch that is turned on when the oil pressure of the oil passage becomes a predetermined value or more is provided between the hydraulic pressure source and the electromagnetic proportional valve,
Until the predetermined time elapses after the steering command means changes from the state in which the minimum target value is instructed to the state in which the target value on the maximum target value side is instructed, the operation control means has the pressure switch turned on. 3. The work vehicle according to claim 1, wherein a driving current obtained by adding a predetermined amount to a current value necessary for maximizing an opening degree of the oil passage is supplied to the electromagnetic proportional valve. Swivel control device.

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