Work vehicle

Abstract

To provide a work vehicle in which a work machine is attached to the rear portion thereof, rear wheels are driven, which prevents floating of the rear wheels and can smoothly travel.SOLUTION: A work vehicle includes a work machine in an ascendsable / descendsable manner in a rear portion of a travel vehicle body, and comprises: control means which can make rear wheels ascend / descend; and rear wheel floating detection means which detects whether the rear wheels are floating from a farm field surface or the rear wheels are about to float from the farm field surface. When a ground load L applied to the rear wheels 5 detected by a load sensor 15 is equal to or less than a first prescribed value L01, the work machine 3 is made to ascend. Then, when the ground load L is equal to or greater than a second prescribed value L02 (L02>L01), the ascending of the work machine 3 is stopped.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a work vehicle capable of switching between four-wheel drive for driving front and rear wheels and two-wheel drive for driving only the front wheels, and having a work implement attached to the rear part of the vehicle.

Background Art

[0002] Patent Document 1 discloses a work vehicle capable of switching between four-wheel drive for driving front and rear wheels and two-wheel drive for driving only the front wheels, and having a work implement such as a tiller attached to the rear part. The work vehicle is configured to detect the ground contact load of the front wheels, and when the ground contact load of the front wheels becomes equal to or less than a predetermined value, it is determined that the front wheels are lifted, and the vehicle is switched from the four-wheel drive state to the two-wheel drive state.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in a work vehicle with a work implement such as a tiller attached to the rear part and rear-wheel drive, when it is necessary to run while strongly pressing the work implement against the field surface in order to till the field, as a result of strongly pressing the work implement against the field surface, the rear wheels, which are the drive wheels, may float and the vehicle may become unable to run.

[0005] Therefore, an object of the present invention is to provide a work vehicle having a work implement attached to the rear part and rear-wheel drive, which can prevent the rear wheels from lifting and can run smoothly.

Means for Solving the Problems

[0006] This object of the present invention is The working machine is provided at the rear of the traveling vehicle body so as to be able to be lifted and lowered, control means for lifting and lowering the rear wheels, and rear wheel lift detection means for detecting whether the rear wheels are lifted from the field surface or are in the process of lifting from the field surface. When the rear wheel lift detection means detects that the rear wheels are lifted from the field surface or are in the process of lifting from the field surface, the control means is configured to lift the working machine. This is achieved by a working vehicle.

[0007] According to the present invention, since the working vehicle is provided with control means for lifting and lowering the rear wheels and rear wheel lift detection means for detecting whether the rear wheels are lifted from the field surface or are in the process of lifting from the field surface, when the rear wheels are lifted from the field surface or are in the process of lifting from the field surface due to the working machine being pressed against the field surface, the control means can lift the working machine and bring the rear wheels into contact with the field surface. Therefore, even when performing tillage work on the field while pressing the working machine against the field surface with a strong force, the working vehicle can be prevented from stopping and the tillage work on the field can be continuously performed.

[0008] In a preferred embodiment of the present invention, after lifting the working machine, when the rear wheel lift detection means detects that the rear wheels are not lifted from the field surface and are not in the process of lifting from the field surface, the control means is configured to stop the lifting of the working machine.

[0009] According to a preferred embodiment of the present invention, when the rear wheel lift detection means detects that the rear wheels are in contact with the field surface, the control means is configured to stop the lifting of the working machine, so that it is possible to promptly resume the tillage work on the field.

[0010] In another preferred embodiment of the present invention, the rear wheel lift detection means is constituted by a rear wheel load sensor for detecting the load applied to the rear wheels.

[0011] In another preferred embodiment of the present invention, the rear-wheel lift detection means is constituted by a rear-wheel rotation speed sensor that detects the rotation speed of the rear wheels.

[0012] In another preferred embodiment of the present invention, the work vehicle further includes a PTO coupling device to which the work implement can be attached, and a PTO clutch that transmits the power of the engine to the PTO coupling device or cuts off the transmission of the power of the engine to the PTO coupling device. The control means controls the PTO clutch so that the transmission of the power of the engine to the PTO coupling device is cut off when the height H of the work implement exceeds a predetermined height H0, and when it is detected by the rear-wheel lift detection means that the rear wheels are lifted off the field surface or are about to be lifted off the field surface, the control means controls the PTO clutch so that the transmission of the power of the engine to the PTO coupling device is not cut off even if the height H of the work implement exceeds the predetermined height H0.

[0013] According to this embodiment, when it is a top priority to bring the rear wheels into contact with the field surface and resume the tilling operation because the rear wheels are lifted off the field surface or are about to be lifted off the field surface, the PTO clutch is controlled so that the power of the engine is transmitted to the PTO coupling device even if the height H of the work implement exceeds the predetermined height H0. Therefore, it is possible to surely prevent the lifting of the work implement from being hindered when the work implement has to be lifted to prevent the rear wheels from lifting.

[0014] In another preferred embodiment of the present invention, the work vehicle further includes a rear cover sensor for detecting the angle of the rear cover, and is configured to raise and lower the work implement so that the angle of the rear cover detected by the rear cover sensor becomes constant. When the rear wheel lift detection means detects that the rear wheels are lifted from the field surface or are about to be lifted from the field surface, it is configured to notify that the work implement is being controlled to rise.

[0015] When the work implement is controlled to move up and down so that the rotation amount of the rear cover becomes constant and tilling is performed at a constant depth, if the rear wheel lift detection means detects that the rear wheels are lifted from the field surface or are about to be lifted from the field surface and controls the work implement to move up and down, it may not be possible to till at a constant depth. However, according to the present embodiment, it becomes possible to know the cause of the inability to till at a constant depth.

Advantages of the Invention

[0016] According to the present invention, it is possible to provide a work vehicle in which a work implement is attached to the rear part and the rear wheels are driven, which can prevent the rear wheels from lifting and can run smoothly.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Mode for Carrying Out the Invention

[0018] Hereinafter, preferred embodiments of the present invention will be examined in detail with reference to the accompanying drawings.

[0019] FIG. 1 is a schematic left side view of a tractor according to a preferred embodiment of the present invention.

[0020] As shown in FIG. 1, the tractor 1 according to the present embodiment includes a body 2, and a tiller 3 is attached to the rear portion of the body.

[0021] In this specification, the “front-rear direction” is the traveling direction when the tractor 1 travels straight, the front side in the traveling direction is referred to as “front”, and the rear side is referred to as “rear”. The “left-right direction” refers to a horizontal direction perpendicular to the front-rear direction. When the operator sits on the driver's seat and faces the front side, the left hand side is referred to as “left” and the right hand side is referred to as “right”.

[0022] As shown in FIG. 1, the body 2 of the tractor 1 has front wheels 4 that are steering wheels and rear wheels 5 that are drive wheels. Power generated by an engine 7 mounted in a bonnet 6 at the front portion of the body 2 is appropriately decelerated and transmitted to the rear wheels 5 by a main transmission unit (not shown in FIG. 1) and an auxiliary transmission unit (not shown in FIG. 1), and is configured to be driven.

[0023] The main transmission unit and the auxiliary transmission unit are housed in a transmission case 20.

[0024] Also, the power generated by the engine 7 and decelerated by the main transmission unit and the sub-transmission unit is configured to be transmitted to the front wheels 4 via a 4WD clutch (not shown in FIG. 1). When power is transmitted from the 4WD clutch to the front wheels 4, the four wheels of the front wheels 3 and the rear wheels 4 are driven by the power transmitted from the engine 7, and a four-wheel drive state is achieved. When the 4WD clutch cuts off the power transmission, only the rear wheels 4 are driven by the power transmitted from the engine 7, and a two-wheel drive state is achieved.

[0025] At the rear part of the body 2 of the tractor 1, a work implement connecting device 8 to which a work implement can be attached is provided. In this embodiment, a tiller 3 is attached as the work implement.

[0026] Also, a driver's seat 9 for operating the tractor 1 is provided at the center of the body 2 of the tractor 1. A steering wheel 10 used for steering the front wheels 3 is provided on the driver's seat 9. The steering wheel 10 is rotatably supported at the upper end of the handle post 11. Also, various operation pedals 12 are provided below the handle post 11.

[0027] A cylinder case 61 is provided at the rear part of the body 2. Lift arms 62 are rotatably provided about the axis AX on both the left and right sides of the cylinder case 61. The lift arms 62 are connected to a lower link 64 via lift rods 63. The tiller 3 is connected to the rear part of the body 2 so as to be liftable by the lower link 64 and the top link 65.

[0028] In this embodiment, a double-acting hydraulic cylinder 61a is provided within a cylinder case 61. Although the detailed structure is not shown in FIG. 1, the internal space of the hydraulic cylinder 61a is divided into two chambers by a piston 61b. When hydraulic pressure is supplied into the chamber on the opposite side (cap side) of the piston rod 61c, in FIG. 1, the piston 61b moves rightward, and the lift arm 62 rotates while ascending around the axis AX. As a result, the lift arm 62 is connected to the lower link 64 via a lift rod 63. Since the tiller 3 is connected to the rear portion of the machine body 2 so as to be liftable by the lower link 64 and the top link 65, the tiller 3 is lifted. As a result, the tiller 3 attached to the lower link 64 and the top link 65 is lifted.

[0029] On the other hand, when hydraulic pressure is supplied into the chamber provided with the piston rod 61c, in FIG. 1, the piston 61c moves leftward, and the lift arm 62 rotates while ascending around the axis AX. As a result, the tiller 3 attached to the lower link 64 and the top link 65 descends.

[0030] In FIG. 1, a lift arm sensor 62a for detecting the rotation angle of the lift arm 62 is provided at the base of the lift arm 62, and the height position of the tiller 3 can be calculated based on the detection value of the lift arm sensor 62a.

[0031] The tiller 3 is a rotary tiller and includes tilling tines 66, a rotary cover 67 that covers the upper side of the tilling tines 66, and a rear cover 68. The tilling tines 66 are configured to be rotated by the power transmitted by the PTO shaft 71 of the PTO connecting device 8 to till the soil in the field. The rear cover 68 is provided rotatably in the vertical direction at the rear of the rotary cover 67, and a rear cover sensor 69 for detecting the angle of the rear cover 68 is provided. The rear cover sensor 69 is constituted by a potentiometer connected to a link interlocked with the rotation of the rear cover 68.

[0032] The height position of the tiller 3 is controlled by rotating the lift arm 62 by a tiller control unit (not shown in FIG. 1) based on the detection value of a tillage depth sensor (not shown in FIG. 1), so that the tillage depth is maintained at a set value.

[0033] FIG. 2 is a block diagram showing the power transmission path of the tractor 1 shown in FIG. 1.

[0034] As shown in FIG. 2, the tractor 1 has, on both the left and right sides of the machine body 2, a left front wheel 4L attached to the left front axle 41L, a right front wheel 4R attached to the right front axle 41R, a left rear wheel 5L attached to the left rear axle 51L, and a left rear wheel 5R attached to the left rear axle 51R.

[0035] Although not shown in FIG. 2, a strain gauge is provided at the rear wheel support portion that supports the rear wheel 5 of the right axle 51R, and a load sensor that detects the ground contact load of the rear wheel 5 is formed.

[0036] As shown in FIG. 2, an engine 7 is mounted at the front part of the machine body 2. The engine 7 is connected to a main transmission portion 302 via a forward and reverse clutch 303, and a sub-transmission portion 304 is arranged at the rear stage of the main transmission portion 302.

[0037] A rear wheel differential gear device 305 is provided at a further rear stage of the sub-transmission portion 304, and brake devices 306L and 306R are respectively provided at the bases of the rear axles 51L and 51R that connect the rear wheel differential gear device 305 and the rear wheels 5.

[0038] Furthermore, the power generated by the engine 7 is input to the transmission shaft 307 via the idle gear and is configured to be transmissible to the front wheels 4 via the 4WD clutch 301 and the front-wheel differential gear device 308. As described above, in this embodiment, when power is transmitted from the 4WD clutch 301 to the front wheels 4, the four wheels of the front wheels 4 and the rear wheels 5 are driven by the power transmitted from the engine 7, entering a four-wheel drive state. When the 4WD clutch 301 cuts off the transmission of power to the front wheels 4, only the rear wheels 5 are driven by the power transmitted from the engine 7, and it is configured to enter a two-wheel drive state. The four-wheel drive state and the two-wheel drive state are switchable.

[0039] Also, a front-wheel steering angle sensor 309 for detecting the steering angle of the front wheels 4 is connected to the travel control unit 100a that controls the travel of the tractor 1. In this embodiment, based on the detection value of the front-wheel steering angle detected by the front-wheel steering angle sensor 309 by the travel control unit 100a, while feedbacking the steering angle of the front wheels 4, the steering cylinder 310 is controlled to configure a so-called automatic travel mode that enables steering.

[0040] The left and right brake devices 306L, 306R provided on the rear wheels 5 are interlocked with the left and right brake pedals 311L, 311R provided on the driver's seat 8. The left brake device 306L provided at the base of the left rear axle 51L is connected to the left brake cylinder 319L, and the right brake device 306R provided at the base of the right rear axle 51R is connected to the right brake cylinder 319R. The left and right brake cylinders 319L, 319R are connected to the left and right brake solenoids 312L, 312R connected to the travel control unit 100a. Therefore, when the operator steps on the brake pedals 311L, 311R, a predetermined brake signal is input to the travel control unit 100a, and the travel control unit 100a drives the brake solenoids 312L, 312R to activate the brake devices 306L, 306R. Here, the brake solenoids 312L, 312R form a hydraulic circuit together with the hydraulic pump 314 and the relief valve 315 via the proportional pressure regulating valve 313.

[0041] As shown in FIG. 2, the tractor 1 is provided with a PTO clutch 316. The PTO clutch 316 is an electronically controlled clutch, and the power from the engine 7 is transmitted to the PTO shaft 71 connected to the tiller 3 by the PTO clutch 316, or the transmission of power to the PTO shaft 71 is blocked. Although not shown, a first PTO speed change shifter and a second PTO speed change shifter are provided on the front stage side of the PTO shaft 71, and by operating these shifters, the PTO shaft 71 can be rotated forward or backward at low speed to high speed.

[0042] FIG. 3 is a hydraulic circuit diagram of the main transmission clutch, the forward and reverse clutch, and the PTO clutch 316.

[0043] In this embodiment, a hydraulic pump 314 operated by the power generated by the engine 7 sucks up the lubricating oil in the transmission case 20 through a suction filter or the like, and pressure oil as hydraulic oil is supplied into the hydraulic circuit.

[0044] As shown in FIG. 3, the tractor 1 is configured such that the pressure contact states of the transmission clutch 317 composed of the first main transmission clutch 317a and the second main transmission clutch 317b, the HI-LO clutch 318, and the forward and reverse clutch 303 can be adjusted. The pressure contact states of such a transmission clutch 317, HI-LO clutch 318, and forward and reverse clutch 303 can be adjusted by controlling the corresponding actuators 201, 202, 203, 204, 205, 206, 207, 208.

[0045] In the first main transmission clutch 317a, the actuator 201 drives the first-speed clutch 321 by the pressure oil supplied through the first-speed solenoid 131, and the actuator 203 drives the third-speed clutch 323 by the pressure oil supplied through the third-speed solenoid 133. Here, the flow rate of the pressure oil supplied to the first main transmission clutch 317a is configured to be adjustable by a 1 / 3-speed boost solenoid 135 that also functions as a proportional control valve.

[0046] In the second main transmission clutch 317b, the actuator 202 drives the second-speed clutch 322 by the pressure oil supplied via the second-speed solenoid 132, and the actuator 204 drives the fourth-speed clutch 324 by the pressure oil supplied via the fourth-speed solenoid 134. Here, the flow rate of the pressure oil supplied to the second main transmission clutch 317b is configured to be adjustable by the 2 / 4-speed boost solenoid 136 that also functions as a proportional control valve.

[0047] In the HI-LO clutch 318, the actuator 205 drives the HI clutch 318a by the pressure oil supplied via the high-speed (HI) boost solenoid 137, and the actuator 206 drives the LO clutch 318b by the pressure oil supplied via the low-speed (LO) boost solenoid 138.

[0048] Also, in the forward / reverse clutch 303, the actuator 207 drives the forward clutch 303a by the pressure oil supplied via the forward switching solenoid 127, and the actuator 208 drives the reverse clutch 303b by the pressure oil supplied via the reverse switching solenoid 129. Here, the flow rate of the pressure oil supplied to the forward clutch 303a and the reverse clutch 303b is configured to be adjustable by the forward / reverse boost solenoid 128 or the clutch pedal solenoid 130.

[0049] Also, the pressing states of the first main transmission clutch 317a, the second main transmission clutch 317b, the HI-LO clutch 318, and the forward and reverse clutch 303, which are driven by the respective actuators 201, 203, 202, 204, 205, 206, 207, 208, are measured by a first-speed clutch pressure sensor 111, a second-speed clutch pressure sensor 112, a third-speed clutch pressure sensor 113, a fourth-speed clutch pressure sensor 114, a high-speed clutch pressure sensor 115, a low-speed clutch pressure sensor 116, a forward clutch pressure sensor 117, and a reverse clutch pressure sensor 118 provided between the respective solenoids 131, 133, 132, 134, 137, 138, 127, 129 and the respective actuators 201, 203, 202, 204, 205, 206, 207, 208. Thereby, the pressing states of the first main transmission clutch 317a, the second main transmission clutch 317b, the Hi-Lo clutch 318, and the forward and reverse clutch 303 can be adjusted.

[0050] As shown in FIG. 3, a double-acting hydraulic cylinder 61a is connected to the hydraulic circuit HCB, and by changing the flow of oil in the hydraulic circuit HCB, the hydraulic cylinder 61a can be expanded and contracted to raise and lower the tiller 3. The hydraulic circuit HCB and the hydraulic cylinder 61a constitute a lifting mechanism for raising and lowering the tiller 3.

[0051] As shown in FIG. 3, the hydraulic circuit HCB includes a work implement raising solenoid 139 and a work implement lowering solenoid 140.

[0052] In the hydraulic circuit HCB, the pressurized oil delivered from the hydraulic pump 314 is supplied via a pressure reducing circuit, a filter, etc. The lifting control unit (not shown in FIGS. 1 to 3) is configured to switch between lowering and rising by outputting a work implement lifting signal toward the work implement rising solenoid 139 and the work implement lowering solenoid 140. For example, when the work implement rising solenoid 139 switches the lifting changeover valve 144 from the neutral position 144a to the rising position 144b, pressurized oil from the hydraulic pump 314 is supplied to the chamber on the side opposite to the side where the piston rod 61 of the hydraulic cylinder 61a is provided (cap side), the hydraulic cylinder 61a extends, and the tiller 3 is raised. Then, when the rising main solenoid 143 returns to the state shown in FIG. 3, the outflow of the pressurized oil sent into the hydraulic cylinder 61a to the hydraulic circuit HCB side is restricted, so the lift arm 62 is held in that position.

[0053] Also, when the work implement lowering solenoid 140 switches the lifting changeover valve 144 from the neutral position 144a to the lowering oil chamber 144c, pressurized oil is supplied to the chamber on the side where the piston rod 61 of the hydraulic cylinder 61a is provided, the hydraulic cylinder 61a contracts, and the tiller 3 descends.

[0054] Note that the work implement lowering solenoid 140 is a proportional solenoid, and the work implement lowering solenoid 140, which is a proportional solenoid, can change the flow rate of the oil supplied to the hydraulic cylinder 61a. Also, the lowering speed of the tiller 3 changes according to the flow rate of the oil supplied to the hydraulic cylinder 61a. For example, if the flow rate is increased, the lowering speed of the tiller 3 becomes faster, but if the flow rate is decreased, the lowering speed of the tiller 3 becomes slower. Thus, the lifting control unit can arbitrarily change the flow rate by the work implement lowering solenoid 140, which is a proportional solenoid, and thereby can arbitrarily change the lowering speed of the tiller 3.

[0055] FIG. 4 is a schematic perspective view in front of the driver's seat 8, FIG. 5 is a schematic perspective view of the portion indicated by A in FIG. 4, and FIG. 6 is a schematic perspective view on the right side of the driver's seat.

[0056] As shown in FIG. 4, a steering wheel 10 attached to a steering post 11 is provided in front of the driver's seat 9. Various operation pedals 12 are provided at the lower part of the steering post 11.

[0057] Specifically, a clutch pedal 325 is provided on the lower left side of the steering post 11, and an accelerator pedal 326 and a brake pedal 311 are provided on the lower right side of the steering post 11. The brake pedal 311 includes left and right brake pedals 311L and 311R.

[0058] A forward and reverse lever 327 is provided on the upper left side of the steering post 11. Also, as shown in FIG. 5, a turn signal lever 328, a throttle lever 329, a lever-type lift switch (one-touch lift lever) 330, etc. are provided on the upper right side of the steering post 11. The lift switch (one-touch lift lever) 330 is a lever that can be moved by one-touch operation when moving the lift arm 62 for connecting the tiller 3 to the operation position or the uppermost position of the position lever. Further, a PTO shift lever or the like is provided on the steering post 11.

[0059] As shown in FIGS. 4 and 5, a PTO switch 331 is provided on the right side of the steering post 10. The PTO switch 331 is a switch operated when connecting or disconnecting the PTO clutch 316 (see FIG. 2). For example, by pushing and turning the PTO switch 331, it is fixed while being pushed in and becomes on. In the on state, by pressing the upper part of the PTO clutch 316, the fixing is released, it automatically rotates, and returns to the original off state.

[0060] A PTO sensitivity switch 332 is provided near the PTO switch 331, and the PTO sensitivity switch 332 is used to adjust the sensitivity (connection time) when the PTO clutch 316 is connected.

[0061] Also, for example, the PTO switch 331 may be provided, as shown in FIG. 6, on the right side of the driver's seat 8 or the like. As shown in FIG. 6, in addition, on the right side of the driver's seat 8, there are provided a main transmission operation unit 333 (main transmission speed increase button 333a, main transmission speed decrease button 333b), a sub transmission lever 334, a button-type lift switch 335 for the tiller 3, a lift lever 336 for the tiller 3, a main transmission switch 337, an accelerator lever 338, and the like. Among these, the lift lever 336 is operated when raising and lowering the lift arm 62 (see FIG. 1) to an arbitrary position.

[0062] Also, as shown in FIG. 4, a dashboard 339 is provided in front of the steering wheel 10, and a meter panel 340, which is a display unit, is provided on the dashboard 339 so as to be visible to the operator sitting on the driver's seat 9.

[0063] The meter panel 340 is provided with a display screen such as a liquid crystal monitor and an engine tachometer (tachometer). On the display screen, a gear position display for displaying the currently selected gear position, and various information such as fuel consumption rate and traveling speed are displayed. Among these, the fuel consumption rate display and the traveling speed display may be displayed so as to automatically switch at regular intervals.

[0064] On the display screen of the meter panel 340, a notification unit for notifying whether or not the tiller 3 (see FIG. 1) mounted on the machine body 2 is in a driving state is provided. The notification unit is, for example, a PTO monitor 341 (see FIG. 7) or a PTO lamp, and is configured to change an image or turn on a lamp, for example, when power is transmitted to the tiller 3, that is, when the tiller 3 is driving. Also, the notification unit may be configured to emit a warning sound or the like when the tiller 3 is driving.

[0065] In the vicinity of the driver's seat 9, for example, on the dashboard 339, an input switch 157 (see FIG. 7) is provided, which is operated when setting the traveling mode of the machine body 2 to the automatic transmission mode (turning on the automatic transmission mode).

[0066] Here, for example, while the tractor 1 is traveling on the road such as moving between fields, it is preferable to perform an accelerator shift (automatic shift), which is a shift control in the main transmission unit 302 (see FIG. 2), based on the operation of depressing the accelerator pedal 326 (see FIG. 4). For this reason, the tractor 1 is configured to be settable to an automatic shift mode by the control unit 100 (see FIG. 7). In the automatic shift mode, the shift stage of the main transmission unit 302 (main transmission clutch 317) is switched according to the detected value of the accelerator pedal sensor 153, the detected value of the vehicle speed sensor 150, and the detected value of the engine rotation sensor 152, which will be described later.

[0067] In this case, the shift stage of the main transmission unit 302 corresponding to the operation amount (depression amount) of the accelerator pedal 326, the vehicle speed (travel speed), and the engine rotation speed is preset, and the set shift stage is stored in the storage unit of the travel control unit 100a. The travel control unit 100a derives the shift stage corresponding to each of the above detected values from the storage unit and switches the shift stage of the main transmission unit 302 to the derived shift stage.

[0068] FIG. 7 is a block diagram showing the control system, detection system, and drive system of the tractor 1 shown in FIGS. 1 to 6.

[0069] In FIG. 7, each of the solenoids 131, 133, 132, 134, 137, 138, 127, 129 related to the shift in FIG. 3 is collectively referred to as a "shift solenoid" and is assigned the reference numeral 120.

[0070] As shown in FIG. 7, the control system of the tractor 1 according to the present embodiment includes a travel control unit 100a that controls the travel of the tractor 1, an engine control unit 100b that controls the engine 7, and a work implement lift control unit 100c that controls the lifting operation of the tiller 3.

[0071] Here, the travel control unit 100a, the engine control unit 100b, and the work implement lift control unit 100c are connected to be able to communicate with each other alternately, for example, to the meter panel 340 via a CAN communication line.

[0072] The traveling control unit 100a is connected to a front-wheel steering angle sensor 309 and a vehicle speed sensor 150, and the detected value of the steering angle of the front wheels 4 detected by the front-wheel steering angle sensor 309 and the detected value of the traveling speed of the tractor 1 detected by the vehicle speed sensor 150 are input to the traveling control unit 100a.

[0073] The traveling control unit 100a is further connected to a shift solenoid 120, a left brake solenoid 312L on the left side, a right brake solenoid 312R on the right side, a proportional pressure regulating solenoid (proportional pressure regulating valve) 313, and a PTO solenoid 151. The traveling control unit 100a is configured to output control signals to the shift solenoid 120, the left brake solenoid 312L on the left side, the right brake solenoid 312R on the right side, the proportional pressure regulating solenoid (proportional pressure regulating valve) 313, and the PTO solenoid 151. Here, the PTO solenoid 151 controls the supply amount of the pressure oil supplied to the PTO clutch 316.

[0074] The engine control unit 100b is connected to an engine rotation sensor 152 and an accelerator pedal sensor 153, and the detected value of the rotation speed of the engine 7 detected by the engine rotation sensor 152 and the depression amount of the accelerator pedal 326 detected by the accelerator pedal sensor 153 are input to the engine control unit 100b.

[0075] As shown in FIG. 7, the work implement lift control unit 100c is connected to a load sensor 15 that detects the ground contact load applied to the rear wheels 5, a lift lever sensor 154 that detects whether or not the lift lever 336 is operated, and a lift switch 335 of the tiller 3. A detection signal of the ground contact load of the rear wheels 5 detected by the load sensor 15, an on / off signal detected by the lift lever sensor 154, and an on / off signal of the lift switch 335 are input to the work implement lift control unit 100c. The lift switch 335 detects the raising operation of the tiller 3 of the work implement raising switch 155 and the lowering operation of the tiller 3 of the work implement lowering switch 156. Note that the one-touch lift lever 330 also has the same configuration as the lift switch 335 to detect the raising and lowering operations of the tiller 3.

[0076] The work implement lift control unit 100c has an up pilot solenoid 144 and a down pilot solenoid 141 connected thereto, and the work implement lift control unit 100c is configured to output a work implement lift signal to the up pilot solenoid 144 and the down pilot solenoid 141 to drive and control a hydraulic cylinder 61a for lifting the work implement.

[0077] When an input switch 157 provided near the driver's seat 9 is turned on, the travel control unit 100a sets the travel mode to the automatic transmission mode. When the travel mode is set to the automatic transmission mode by the travel control unit 100a, the tractor 1 automatically shifts gears by depressing the accelerator pedal 326. In the automatic transmission mode, the tractor 1 is automatically shifted based on the travel speed of the vehicle body 2 detected by a vehicle speed sensor 150 and input to the travel control unit 100a, the depression amount (depression position) of the accelerator pedal 326 detected by an accelerator pedal sensor 153 and input to the engine control unit 100b, and the engine speed detected by an engine speed sensor 152 and input to the engine control unit 100b.

[0078] In the work vehicle 1 according to the present embodiment, the work implement lift control unit 100c constantly monitors the height position H of the tiller 3, and when the height position H of the tiller 3 exceeds a predetermined height H0, the PTO clutch 316 is controlled so that the power from the engine 7 is not transmitted to the PTO shaft 71 connected to the tiller 3.

[0079] That is, the rotation angle of the lift arm 62 detected by the lift arm sensor 62a is input to the work implement lift control unit 100c, and the work implement lift control unit 100c calculates the height position H of the tiller 3 based on the rotation angle of the lift arm 62 input to the travel control unit 100a. When it is determined that the height H of the tiller 3 exceeds a predetermined height H0, a cutoff signal is output to the PTO clutch 316 to control the PTO clutch 316 so that the power from the engine 7 is not transmitted to the PTO shaft 71.

[0080] The tractor 1 according to this embodiment configured as described above tills the field with the tiller 3 as follows.

[0081] First, the engine 7 is started, and the power generated by the engine 7 is decelerated by the main transmission unit 302 and the sub - transmission unit 304 and input to the 4WD clutch 301. In the normal state of traveling on flat ground, the 4WD clutch 301 is configured to transmit the power generated by the engine 7 and decelerated by the main transmission unit and the sub - transmission unit to the front wheels 4. Together with the rear wheels 5, the front wheels 4 are also driven, and the tractor 1 travels by four - wheel drive.

[0082] When using the tiller 3 to till the field, the operator turns on the tiller lowering switch 156 so that the tilling claws 66 are positioned within the soil of the field, and the tiller 3 is pressed against the field surface.

[0083] In this way, when tilling the field, while the tractor 1 travels while the tilling claws 66 dug into the soil of the field dig up the soil of the field, when the surface of the field is hard like that of a field in the People's Republic of China, it is difficult to push the tilling claws 66 into the soil of the field, so it is necessary to press the tilling claws 66 against the soil surface with a strong force.

[0084] Therefore, in this embodiment, a double - acting hydraulic cylinder 61a is used to configure the tiller 3 to be lifted and lowered.

[0085] However, when configured to press the tiller 3 against the field surface with a strong force using such a double - acting hydraulic cylinder 61a, the force pressing the tiller 3 against the soil surface of the field may cause the rear wheels 5, which are the drive wheels, to lift off the field surface and continuously become unable to travel.

[0086] Therefore, in the present embodiment, when the rear wheel 5 is lifted off the field surface or is about to be lifted off the field surface, the tiller 3 is lifted to be separated from the field surface, and the rear wheel 5 is brought into contact with the field surface so as to enable smooth travel.

[0087] Specifically, during the tilling of the field, when the working implement lift control unit 100c determines based on the detection signal of the ground contact load of the rear wheel 5 detected by the load sensor 15 that the ground contact load L applied to the rear wheel 5 has become equal to or less than the first predetermined value L01, since the force pushing the tiller 3 into the soil is excessive and there is a possibility that the rear wheel 5 has lifted off the field surface or is about to lift off, the working implement lift control unit 100c outputs a working implement lift signal to the lift pilot solenoid 144, supplies hydraulic oil to the hydraulic cylinder 61a, and rotates the lift arm 62 while lifting it around the axis AX to lift the tiller 3. In the present embodiment, when the tiller 3 exceeds the predetermined height H0, the working implement lift control unit 100c outputs a cutoff signal to the PTO clutch 316 to control the PTO clutch 316 so that the power from the engine 7 is not transmitted to the PTO shaft 71. However, when a working implement lift signal is output from the working implement lift control unit 100c to the lift pilot solenoid 144, even if the tiller 3 exceeds the predetermined height H0, the working implement lift control unit 100c is configured not to output a cutoff signal to the PTO clutch 316.

[0088] As a result, the rear wheel 5, which had been lifted off the field surface or was about to be lifted off due to the tiller 3 being pressed against the field surface with a strong force, descends and comes into contact with the field surface.

[0089] In this way, even after the rear wheel 5 comes into contact with the field surface, the implement lift control unit 100c continues to monitor the ground contact load L applied to the rear wheel 5 detected by the load sensor 15. When it is determined that the ground contact load L applied to the rear wheel 5 detected by the load sensor 15 is equal to or greater than a second predetermined value L02 (where L02 > L01), since it is recognized that the rear wheel 5 is in complete contact with the field surface, an implement stop signal is output to the lift pilot solenoid 144 to stop the supply of hydraulic oil to the hydraulic cylinder 61a and stop the ascent of the tiller 3.

[0090] Thereafter, when a predetermined time T0 has elapsed, the implement lift control unit 100c outputs an implement lift signal to the lowering pilot solenoid 141 to supply pressure oil into the chamber provided with the piston rod 61c of the hydraulic cylinder 61a, and rotates the lift arm 62 while lowering it around the axis AX to lower the tiller 3 and bring it into contact with the field surface.

[0091] As a result, since the tilling claws 66 of the tiller 3 can be pressed against the soil surface with a predetermined force, the tilling operation of the field can be resumed using the tiller 3.

[0092] When the tractor 1 is driven while strongly pressing the tiller 3 against the field surface to till the field, if the field is hard, the rear wheel 5 may lift off the field surface and it may become impossible to drive. However, according to the present embodiment, when the implement lift control unit 100c determines that the ground contact load L applied to the rear wheel 5 detected by the load sensor 15 is equal to or less than a first predetermined value L01, it is determined that the rear wheel 5 has lifted off the field surface or there is a risk of lifting off, and an implement ascent signal is output to the lift pilot solenoid 144 to supply hydraulic oil to the hydraulic cylinder 61a, and the lift arm 62 is rotated while being lifted around the axis AX to lift the tiller 3. Therefore, the rear wheel 5 can be lowered toward the field surface and brought into contact with the field surface.

[0093] Furthermore, when it is determined that the ground contact load L applied to the rear wheels 5 detected by the load sensor 15 has reached a second predetermined value L02 (where L02 > L01), the work implement lifting control unit 100c determines that the rear wheels 5 have come into complete contact with the field surface, outputs a work implement stop signal to the lift pilot solenoid 144, stops the supply of hydraulic oil to the hydraulic cylinder 61a, and stops the upward movement of the tiller 3.

[0094] After that, when a predetermined time T0 has elapsed, the work implement lifting control unit 100c outputs a work implement lifting signal to the lowering pilot solenoid 141, supplies pressure oil into the chamber provided with the piston rod 61c of the hydraulic cylinder 61a, rotates the lift arm 62 while lowering it around the axis AX, lowers the tiller 3, and brings it into contact with the field surface.

[0095] As a result, since the tilling claws 66 of the tiller 3 can be pressed against the soil surface with a predetermined force, the tilling operation of the field can be restarted using the tiller 3.

[0096] As described above, according to the present embodiment, since the double-acting hydraulic cylinder 61a is used, even if the field surface is hard, the tilling operation can be performed while strongly pressing the tiller 3 against the field surface. On the other hand, as a result of strongly pressing the tiller 3 against the field surface and running the tractor 1, even when the rear wheels 5 are likely to lift off from the field, it is effectively prevented that the rear wheels 5 lift off and the tilling operation of the field becomes impossible, and the tractor 1 can smoothly till the field.

[0097] FIG. 8 is a block diagram showing a control system, a detection system, and a drive system of a tractor according to another preferred embodiment of the present invention.

[0098] In FIG. 8, instead of the load sensor 15 in FIG. 7 that detects the ground contact load applied to the rear wheels 5, a rear wheel rotation speed sensor 25 that detects the rotation speed of the rear wheels 5 is provided.

[0099] The rotational speed of the rear wheel 5 detected by the rear wheel rotational speed sensor 25 is input to the implement lift control unit 100c. The implement lift control unit 100c calculates a change rate ΔV of the rotational speed of the rear wheel 5 based on the input rotational speed of the rear wheel 5. As a result, when the change rate ΔV of the rotational speed of the rear wheel 5 exceeds a first predetermined value ΔV1, it is recognized that the rear wheel 5 is spinning idly. Therefore, the implement lift control unit 100c determines that the rear wheel 5 is lifted from the field surface or is about to be lifted from the field surface, outputs an implement lift signal to the lift pilot solenoid 144, supplies hydraulic pressure into the chamber on the side where the piston rod 61c of the hydraulic cylinder 61a is not provided, and rotates the lift arm 62 while raising it around the axis AX to raise the tiller 3.

[0100] Accordingly, since the tiller 3 was pressing against the field surface with a strong force, the rear wheel 5 that had been lifted from the field surface or was about to be lifted descends and comes into contact with the field surface.

[0101] Thus, even after the rear wheel 5 comes into contact with the field surface, the implement lift control unit 100c continues to monitor the rotational speed of the rear wheel 5 detected by the rear wheel rotational speed sensor 25. When it is determined that the change rate ΔV of the rotational speed of the rear wheel 5 has become equal to or less than a second predetermined value ΔV2 (ΔV2 < ΔV1), it can be determined that the rear wheel 5 is completely in contact with the field surface. Therefore, an implement stop signal is output to the lift pilot solenoid 144, the supply of pressure oil into the chamber on the side where the piston rod 61c of the hydraulic cylinder 61a is not provided is stopped, and the raising of the tiller 3 is stopped.

[0102] As a result, by driving the rear wheel 5, the tractor 1 can travel on the field surface.

[0103] Thereafter, when a predetermined time T0 has elapsed, the implement lift control unit 100c outputs an implement lift / lower signal to the lower pilot solenoid 141, supplies pressure oil into the chamber where the piston rod 61c of the hydraulic cylinder 61a is provided, and rotates the lift arm 62 while lowering it around the axis AX to lower the tiller 3 and bring it into contact with the field surface.

[0104] Therefore, since the tilling claws 66 of the tiller 3 can be pressed against the soil surface with a predetermined force, the tilling operation of the field can be restarted using the tiller 3.

[0105] Also in this embodiment, when the change rate ΔV of the rotational speed of the rear wheels 5 becomes equal to or greater than a first predetermined value ΔV1, the work implement lift control unit 100c determines that the rear wheels 5 are starting to lift off the field surface or that the rear wheels 5 are starting to lift off the field surface, and raises the tiller 3. After raising the tiller 3, when it is determined that the change rate ΔV of the rotational speed of the rear wheels 5 has become equal to or less than a second predetermined value ΔV2 (ΔV2 < ΔV1), the work implement lift control unit 100c determines that the rear wheels 5 are in contact with the field surface, lowers the tiller 3, brings it into contact with the field surface, and is configured to restart the tilling operation. Therefore, even when tilling the field while pressing the tiller 3 against a hard field surface, it is possible to surely prevent the rear wheels 5 from lifting off the field surface and making smooth travel impossible.

[0106] FIG. 9 is a block diagram showing a control system, a detection system, and a drive system of a tractor according to still another preferred embodiment of the present invention.

[0107] In this embodiment, as shown in FIG. 9, the work vehicle 1 is provided with a rear cover sensor 69 that detects the angle of the rear cover 68.

[0108] Since the rear cover 68 rises when the tilling depth of the field by the tiller 3 is deep and descends when the tilling depth is shallow, if the work implement lift control unit 100c controls the raising and lowering of the tiller 3 so that the amount of rotation of the rear cover 68 becomes constant, it becomes possible to till the field at a constant depth.

[0109] However, in the present embodiment, when the ground contact load L of the rear wheels 5 detected by the load sensor 15 becomes equal to or less than the first predetermined value L01, the work implement lift control unit 100c determines that the rear wheels 5 are lifted from the field surface or there is a possibility that they are about to be lifted. Then, the tiller 3 is lifted and the rear wheels 5 are lowered. After that, when it is determined that the ground contact load L applied to the rear wheels 5 detected by the load sensor 15 becomes equal to or greater than the second predetermined value L02 (where L02 > L01), it is determined that the rear wheels 5 are in complete contact with the field surface, and the lift of the tiller 3 is configured to stop. Therefore, even when the field is being tilled so that the rotation amount of the rear cover is constant and the tilling depth is constant, the tiller 3 may be lifted and the rotation amount of the rear cover 68 detected by the rear cover sensor 69 may change. Thus, when the ground contact load L of the rear wheels 5 detected by the load sensor 15 becomes equal to or less than the first predetermined value L01, the work implement lift control unit 100c is configured to display on the display screen of the meter panel 340 that the tiller 3 is being lifted and the tilling depth is changing.

[0110] The present invention is not limited to the above embodiments, and various modifications can be made within the scope of the invention described in the claims. Needless to say, these are also included within the scope of the present invention.

[0111] For example, in the above embodiment, the tiller 3 is used as the work implement, but it is not necessarily required to use the tiller 3 as the work implement, and the work machine may be provided with a work implement other than the tiller 3.

[0112] Furthermore, in the embodiments shown in FIGS. 1 to 7, a load sensor 15 for detecting the load applied to the rear wheels 5 is used to determine whether the rear wheels 5 are lifted off the field surface or are in the process of being lifted. In the embodiment shown in FIG. 8, a rear wheel rotation speed sensor 25 for detecting the rotation speed of the rear wheels 5 is used to determine whether the rear wheels 5 are lifted off the field surface or are in the process of being lifted. However, it is not necessarily required to determine whether the rear wheels 5 are lifted off the field surface or are in the process of being lifted using the load sensor 15 or the rear wheel rotation speed sensor 25. It may also be determined by other methods whether the rear wheels 5 are lifted off the field surface or are in the process of being lifted.

[0113] Also, in the embodiment shown in FIG. 8, the rotation speed of the rear wheels 5 is detected using the rear wheel rotation speed sensor 25 for detecting the rotation speed of the rear wheels 5. However, if the vehicle speed sensor 150 used in the embodiments shown in FIGS. 1 to 7 is configured to obtain the vehicle speed of the tractor 1 based on the rotation speed of the rear wheels 5, then the rotation speed of the rear wheels 5 may be detected based on the vehicle speed sensor 150, and it is not necessary to use the rear wheel rotation speed sensor 115.

Explanation of Reference Numerals

[0114] 1 Tractor 2 Body 3 Cultivator 4 Front Wheels 4L Left Front Wheel 4R Right Front Wheel 5 Rear Wheels 5L Left Rear Wheel 5R Right Rear Wheel 6 Bonnet 7 Engine 8 PTO Connecting Device 10 Steering Wheel 11 Steering Column 12 Operation Pedal 15 Load Sensor 25 Rear Wheel Rotation Speed Sensor 41L Left Front Axle 41R Right Front Axle Rear axle on the left side of 51L Rear axle on the right side of 51R Cylinder case 61 Double-acting hydraulic cylinder 61a Piston 61b Piston rod 61c Lift arm 62 Lift arm sensor 62a Lift rod 63 Lower link 64 Top link 65 Tillage claw 66 Rotary cover 67 Rear cover 68 Rear cover sensor 69 PTO shaft 71 Travel control unit 100a Engine control unit 100b Implement lift control unit 100c 1st gear clutch pressure sensor 111 2nd gear clutch pressure sensor 112 3rd gear clutch pressure sensor 113 4th gear clutch pressure sensor 114 High-speed clutch pressure sensor 115 Low-speed clutch pressure sensor 116 Forward clutch pressure sensor 117 Reverse clutch pressure sensor 118 Shift solenoid 120 Forward switching solenoid 127 Forward and reverse boost solenoid 128 Reverse switching solenoid 129 Clutch pedal solenoid 130 3rd gear solenoid 133 4th gear solenoid 134 1, 3rd gear boost solenoid 135 2, 4th gear boost solenoid 136 High-speed (HI) boost solenoid 137 Implement lift solenoid 139 Implement lower solenoid 140 Lower pilot solenoid 141 141a and 141b oil chambers 142 Lowering main solenoid 143 Rising main solenoid 144 Rising pilot solenoid 145 Check valve 146 Slow return valve 150 Vehicle speed sensor 151 PTO solenoid 152 Engine speed sensor 153 Accelerator pedal sensor 155 Implement lift switch 156 Implement lower switch 157 Input switch 201, 202, 203, 204, 205, 206, 207, 208 Actuators 301 4WD clutch 302 Main transmission section 303 Forward and reverse clutch 304 Auxiliary transmission section 305 Rear wheel differential gear device 306L and 306R Brake devices 307 Transmission shaft 308 Front wheel differential gear device 309 Front wheel steering angle sensor 310 Steering cylinder 311L and 311R Brake pedals 312L and 312R Brake solenoids 313 Proportional pressure regulating valve 314 Hydraulic pump 315 Relief valve 316 PTO clutch 317 Transmission clutch 317a Main first main transmission clutch 317b Second main transmission clutch 318 HI-LO clutch 318a HI clutch 318b LO clutch 319L Left brake cylinder 319R Right brake cylinder 321 1-speed clutch 322 2-speed clutch 323 3-speed clutch 324 4-speed clutch 326 Accelerator pedal 330 One-touch lift lever 331 PTO switch 332 PTO sensitivity switch 333 Main transmission operation unit 333a Main transmission speed increase button 333b Main transmission speed decrease button 334 Auxiliary transmission lever 335 Button-type lift switch 336 Cultivator lift lever 337 Main transmission switch 338 Accelerator lever 339 Dashboard 340 Meter panel 341 PTO monitor

Claims

Claim 1: A work vehicle having a front wheel and a rear wheel, and a work implement is provided at the rear part of the traveling vehicle body so as to be liftable, control means for controlling the lifting operation of the work implement, a rear wheel lift detection means for detecting whether the rear wheel is lifted from the field surface or the rear wheel is being lifted from the field surface, a work vehicle configured such that when the rear wheel lift detection means detects that the rear wheel is lifted from the field surface or the rear wheel is being lifted from the field surface, the control means raises the work implement, the work vehicle further having a PTO connection device to which the work implement can be attached, and the power of the engine is transmitted to the PTO connection device, or a PTO clutch for blocking the transmission of the power of the engine to the PTO connection device, and the control means, when the height of the work implement exceeds a predetermined height, controls the PTO clutch so that the transmission of the power of the engine to the PTO connection device is blocked, and when the rear wheel lift detection means detects that the rear wheel is lifted from the field surface or the rear wheel is being lifted from the field surface, the control means controls the PTO clutch so that the transmission of the power of the engine to the PTO connection device is not blocked even if the height of the work implement exceeds the predetermined height. A work vehicle characterized by being configured as described above.

2. The work vehicle further includes a rear cover sensor for detecting the angle of the rear cover, and the work implement is lifted so that the angle of the rear cover detected by the rear cover sensor becomes constant, and when the rear wheel lift detection means detects that the rear wheel is lifted from the field surface or the rear wheel is being lifted from the field surface, it is configured to notify that the work implement is being controlled to be lifted. A work vehicle according to claim 1, characterized by being configured as described above. ​ ​

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