Agricultural tractor

Abstract

To provide an agricultural tractor that can forcibly lower a ground working machine by a pressure caused by a hydraulic device.SOLUTION: An agricultural tractor comprises lift arms 72L and 72R for lifting and lowering a ground working machine fitted to a connection device 7 of a traveling vehicle body rear part, a main cylinder mechanism 77, and an auxiliary cylinder mechanism 95. Pressure oil is supplied to the main cylinder mechanism 77 and the auxiliary cylinder mechanism 95, and thereby the lift arms 72L and 72R are lifted and rotated. The pressure oil is supplied to the auxiliary cylinder mechanism 95, and thereby the lift arms 72L and 72R are lowered and rotated.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention is oil is provided with a pressure lifting and lowering device, An agricultural tractor that raises and lowers a working implement to perform ground operations and relates to

Background Art

[0002] A lift arm for lifting a working machine connected to a conventional agricultural tractor rotates up and down by a main cylinder mechanism provided in a hydraulic cylinder case above the transmission case. In addition to this configuration, a configuration is known that includes an auxiliary cylinder mechanism directly connected to the lift arm for the purpose of increasing hydraulic pressure (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in Patent Document 1, During descent, it descends under the weight of the working implement, and the oil circuit on the ascending side communicates with the tank to discharge pressure oil. However, when performing ground operations such as tilling on hard ground, the working implement may be pushed up due to the hardness of the ground, resulting in shallower ground operations

[0005] The present invention In view of the above, an object is to provide an agricultural tractor in which a ground working implement can be forcibly lowered by the pressure of hydraulic equipment 。

Means for Solving the Problems

[0006] To solve the above problems, the present invention has taken the following technical means.

[0007] The invention according to claim 1 It includes lift arms (72L, 72R) for raising and lowering a ground working implement mounted on a connecting device (7) at the rear of a traveling vehicle body, a main cylinder mechanism (77), and an auxiliary cylinder mechanism (95). When pressure oil is supplied to the main cylinder mechanism (77) and the auxiliary cylinder mechanism (95), the lift arms (72L, 72R) are rotated upward, and when pressure oil is supplied to the auxiliary cylinder mechanism (95), the lift arms (72L, 72R) are rotated downward is characterized by

[0008] Also, an auxiliary cylinder control valve unit (100) is provided between the pump (70) and the auxiliary cylinder mechanism (95), and a first control valve (108) for selecting whether or not to supply pressure oil to the auxiliary cylinder mechanism (95) when the lift arms (72L, 72R) are rotated downward is provided in the auxiliary cylinder control valve unit (100).

[0009] Also , an auxiliary cylinder control valve unit (100) is provided between the pump (70) and the auxiliary cylinder mechanism (95), the auxiliary cylinder control valve unit (100) and the auxiliary cylinder mechanism (95) are connected by an oil passage (107), the auxiliary cylinder control valve unit (100) includes a second control valve (109), when the lift arms (72L, 72R) are rotated upward, the main cylinder mechanism (77) and the auxiliary cylinder mechanism (95) are provided in parallel in the hydraulic circuit and are supplied with pressure oil simultaneously, and the second control valve (109) connects the oil passage (107) and the tank to discharge the return oil from the auxiliary cylinder mechanism (95), when the lift arms (72L, 72R) are rotated downward, the oil passage (107) and the pump (70) are connected to supply pressure oil to the auxiliary cylinder mechanism (95).

Effect of the Invention

[0010] According to the present invention, Since the auxiliary cylinder mechanism can forcibly lower the ground working implement, ground operations can be performed without being affected by the hardness of the ground even on hard ground .

Brief Description of the Drawings

[0011]

Figure 1

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Figure 5

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Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0013] The tractor 1 of the present embodiment shown in FIGS. 1 to 4 is an agricultural tractor that performs work in a field or the like while self-propelling by the power generated by a power source. The tractor 1 includes front wheels 2, rear wheels 3, an engine 4 as a power source, and a transmission 5. Among these, the front wheels 2 are mainly provided as steering wheels, that is, steering wheels. The rear wheels 3 are mainly provided as driving wheels, that is, drive wheels. The rear wheels 3 can transmit the rotational power generated by the engine 4 mounted in the bonnet 6 at the front of the machine body to the transmission 5 and appropriately decelerate it, and the rear wheels 3 generate a driving force by this rotational power. Further, this transmission 5 can also transmit the rotational power generated by the engine 4 to the front wheels 2 as necessary. In this case, all four wheels of the front wheels 2 and the rear wheels 3 become drive wheels and generate a driving force. That is, the transmission 5 can switch between two-wheel drive and four-wheel drive, decelerate the rotational power of the engine 4, and transmit the decelerated rotational power to the front wheels 2 and the rear wheels 3. Further, the tractor 1 is provided with a connecting device 7 (also referred to as a three-point link connecting device) at the rear of the machine body to which a working machine such as a rotary (not shown) can be attached. The connecting device 7 is, for example, a three-point link composed of a top link 7a at the upper center and lower left and right lower links 7b, 7b, and connects a working machine to the rear of the machine body of the tractor 1. The tractor 1 can raise and lower the working machine through a lift rod and a lower link 7b or the like connected to this lift rod by rotating the left and right lift arms hydraulically as described later.

[0014] The periphery of the driver's seat 8 on the machine body of the tractor 1 is covered by a cab 9. Inside the cab 9 of the tractor 1, a steering wheel 11 stands upright from a dashboard 10 on the front side of the driver's seat 8, and various operation pedals such as a clutch pedal, a brake pedal, and an accelerator pedal, and various operation levers such as a forward and reverse lever and a shift lever are arranged around the driver's seat 8.

[0015] FIG. 5 is a diagram showing a transmission mechanism 13 in a transmission case 12 of a transmission 5. The transmission 5 includes a transmission case 12 (see FIG. 1) and a transmission mechanism 13 disposed in the transmission case 12 for transmitting rotational power from the engine 4 to the rear wheels 3 and the like. The transmission mechanism 13 transmits the rotational power from the engine 4 to the front wheels 2, the rear wheels 3, and a working machine mounted on the machine body, and drives these by the rotational power from the engine 4.

[0016] Specifically, the transmission mechanism 13 includes an input shaft 14, a forward / reverse switching mechanism 15, a Hi-Lo transmission mechanism 16 as a high / low speed transmission mechanism, a main transmission mechanism 17, a sub-transmission mechanism 18, a 2WD / 4WD switching mechanism 19, a PTO drive mechanism 20, and the like. The transmission mechanism 13 can transmit the rotational power generated by the engine 4 to the rear wheels 3 through the input shaft 14, the forward / reverse switching mechanism 15, the Hi-Lo transmission mechanism 16, the main transmission mechanism 17, and the sub-transmission mechanism 18 in sequence. Also, the transmission mechanism 13 can transmit the rotational power generated by the engine 4 to the front wheels 2 through the input shaft 14, the forward / reverse switching mechanism 15, the Hi-Lo transmission mechanism 16, the main transmission mechanism 17, the sub-transmission mechanism 18, and the 2WD / 4WD switching mechanism 19 in sequence. Further, the transmission mechanism 13 can transmit the rotational power generated by the engine 4 to the working machine through the input shaft 14 and the PTO drive mechanism 20 in sequence.

[0017] The input shaft 14 is coupled to the output shaft of the engine 4, and the rotational power from the engine 4 is input.

[0018] The forward and reverse switching mechanism 15 can switch the rotational power transmitted from the engine 4 between forward rotation and reverse rotation. The forward and reverse switching mechanism 15 includes a forward gear stage 15a, a reverse gear stage 15b, a reverse counter gear 15c (also referred to as a reverse gear), a forward hydraulic multi-plate clutch C1 in the form of a hydraulic multi-plate clutch, and a reverse hydraulic multi-plate clutch C2. The forward and reverse hydraulic multi-plate clutches C1 and C2 can switch the power transmission path in the forward and reverse switching mechanism 15 by switching between the engaged / released states. The forward and reverse switching mechanism 15 transmits the rotational power transmitted to the input shaft 14 to the counter shaft 21 by changing the transmission path according to the engaged / released states of the forward and reverse hydraulic multi-plate clutches C1 and C2.

[0019] When the forward hydraulic multi-plate clutch C1 is in the engaged state and the reverse hydraulic multi-plate clutch C2 is in the released state, the forward and reverse switching mechanism 15 transmits the rotational power transmitted to the input shaft 14 to the counter shaft 21 in the forward rotation direction via the forward gear stage 15a and the forward hydraulic multi-plate clutch C1. When the forward hydraulic multi-plate clutch C1 is in the released state and the reverse hydraulic multi-plate clutch C2 is in the engaged state, the forward and reverse switching mechanism 15 transmits the rotational power transmitted to the input shaft 14 to the counter shaft 21 in the reverse rotation direction via the reverse gear stage 15b, the reverse gear 15c, and the reverse hydraulic multi-plate clutch C2. Thereby, the forward and reverse switching mechanism 15 can switch the forward and reverse of the tractor 1.

[0020] Also, the forward and reverse switching mechanism 15 also functions as a main clutch. By setting both the forward and reverse hydraulic multi-plate clutches C1 and C2 to the released state, it enters the neutral state and can cut off the power transmission to the front wheels 2 and the rear wheels 3. The forward and reverse switching mechanism 15 can be switched between forward, reverse, and neutral by hydraulic control, for example, by an operator operating a forward and reverse switching lever (not shown). Also, by stepping on the clutch pedal, both the forward and reverse hydraulic multi-plate clutches C1 and C2 can be set to the released state.

[0021] The Hi-Lo speed change mechanism 16 is capable of changing the rotational power transmitted from the engine 4 at a high speed stage or a low speed stage. The Hi-Lo speed change mechanism 16 includes a Hi (high speed) side gear stage 16a, a Lo (low speed) side gear stage 16b, a hydraulic multi-plate clutch (Hi (high speed) side clutch) C3, and a hydraulic multi-plate clutch (Lo (low speed) side clutch) C4. The hydraulic multi-plate clutches C3 and C4 can switch the power transmission path in the Hi-Lo speed change mechanism 16 by switching the engaged / released state. The Hi-Lo speed change mechanism 16 transmits the rotational power transmitted to the countershaft 21 to the transmission shaft 22 by changing the transmission path according to the engaged / released state of the hydraulic multi-plate clutches C3 and C4. When the hydraulic multi-plate clutch C3 is in the engaged state and the hydraulic multi-plate clutch C4 is in the released state, the Hi-Lo speed change mechanism 16 transmits the rotational power transmitted to the countershaft 21 through the hydraulic multi-plate clutch C3 and the Hi side gear stage 16a after shifting to the transmission shaft 22.

[0022] When the hydraulic multi-plate clutch C3 is in the released state and the hydraulic multi-plate clutch C4 is in the engaged state, the Hi-Lo speed change mechanism 16 transmits the rotational power transmitted to the countershaft 21 through the hydraulic multi-plate clutch C4 and the Lo side gear stage 16b after shifting to the transmission shaft 22. Thereby, the Hi-Lo speed change mechanism 16 can change the rotational power from the engine 4 at the gear ratio of the Hi side gear stage 16a or the gear ratio of the Lo (low speed) side gear stage 16b and transmit it to the subsequent stage. The Hi-Lo speed change mechanism 16 can be switched between the Hi (high speed) side and the Lo (low speed) side by hydraulic control, for example, when an operator turns on / off a Hi-Lo changeover switch (high-low speed operation switch) not shown in the figure, and can shift at either of the two speeds of high speed and low speed. Further, the Hi-Lo speed change mechanism 16 can be shifted during the running of the tractor 1 with the above configuration.

[0023] The main transmission mechanism 17 can shift the rotational power transmitted from the engine 4 at any of a plurality of shift speeds. The main transmission mechanism 17 is a synchromesh type transmission mechanism, and here, it can shift the rotational power transmitted from the engine 4 via the forward and reverse switching mechanism 15 and the Hi-Lo transmission mechanism 16. The main transmission mechanism 17 is configured to include a first-speed gear stage 17a, a second-speed gear stage 17b, a third-speed gear stage 17c, a fourth-speed gear stage 17d, a fifth-speed gear stage 17e, and a sixth-speed gear stage 17f as a plurality of shift speeds. The main transmission mechanism 17 shifts the rotational power transmitted to the transmission shaft 22 through any one of the first-speed gear stage 17a to the sixth-speed gear stage 17f according to the coupling state with the transmission shaft 22 of the first-speed gear stage 17a to the sixth-speed gear stage 17f, and transmits it to the transmission shaft 23. Thereby, the main transmission mechanism 17 can shift the rotational power from the engine 4 at any gear ratio of the first-speed gear stage 17a to the sixth-speed gear stage 17f and transmit it to the subsequent stage. The main transmission mechanism 17 can be selected and switched to one of a plurality of shift speeds, for example, by an operator operating the main transmission operation lever, and can shift at any of the six speeds of the first-speed gear stage 17a to the sixth-speed gear stage 17f. Further, the main transmission mechanism 17 can be shifted during the running of the tractor 1 with the above configuration.

[0024] The auxiliary transmission mechanism 18 can shift the rotational power transmitted from the engine 4 in sequence through the forward and reverse switching mechanism 15, the Hi-Lo transmission mechanism 16, and the main transmission mechanism 17. The auxiliary transmission mechanism 18 is configured to include a first auxiliary transmission 24, a second auxiliary transmission 25, etc., and shifts the rotational power transmitted to the transmission shaft 23 through the first auxiliary transmission 24, the second auxiliary transmission 25, etc., and transmits it to the transmission shaft 26. The first auxiliary transmission 24 can shift the rotational power transmitted from the engine 4 and shifted by the main transmission mechanism 17, etc., at a high speed stage or a low speed stage and transmit it to the rear wheel 3 side which is a driving wheel. The second auxiliary transmission 25 can shift the rotational power transmitted from the engine 4 and shifted by the main transmission mechanism 17, etc., at an ultra-low speed stage which is even lower than the first auxiliary transmission 24 and transmit it to the rear wheel 3 side which is a driving wheel. Note that the second auxiliary transmission 25 is omitted when simplification of specifications, etc., is required.

[0025] The first subtransmission 24 of the subtransmission mechanism 18 includes a first gear 24a, a second gear 24b, a third gear 24c, a fourth gear 24d, and a shifter 24e. The first gear 24a is integrally rotatably coupled to the transmission shaft 23, and the rotational power from the transmission shaft 23 is transmitted (input). The second gear 24b meshes with the first gear 24a. The third gear 24c is integrally rotatably coupled to the second gear 24b. The fourth gear 24d meshes with the third gear 24c. The shifter 24e switches the coupling state between the first gear 24a, the fourth gear 24d, and the transmission shaft 26. That is, a clutch claw 26a provided integrally with the transmission shaft 26, a clutch claw 24ac integrally formed with the first gear 24a, and a clutch claw 24dc integrally formed with the fourth gear 24d are formed with the same diameter and the same number of teeth and are arranged in an adjacent state. When the shifter 24e simultaneously engages the clutch claw 26a and the clutch claw 24ac, power is transmitted from the first gear 24a to the transmission shaft 26, and when the clutch claw 26a and the clutch claw 24dc are simultaneously engaged, power is transmitted from the fourth gear 24d to the transmission shaft 26. The shifter 24e is configured to be shiftable to a position where it does not engage with either the clutch claw 24ac or the clutch claw 24dc.

[0026] The shifter 24e can move to a Hi (high speed) side position where the first gear 24a and the transmission shaft 26 are integrally rotatably coupled, a Lo (low speed) side position where the fourth gear 24d and the transmission shaft 26 are integrally rotatably coupled, and a neutral position (neutral position) where neither the first gear 24a nor the fourth gear 24d is coupled to the transmission shaft 26 and is released. The first subtransmission 24 transmits the rotational power transmitted to the transmission shaft 23 to the transmission shaft 26 by switching the transmission path according to the position of the shifter 24e.

[0027] The second auxiliary transmission 25 of the auxiliary transmission mechanism 18 includes a first gear 25a, a second gear 25b, a third gear 25c, a fourth gear 25d, and a shifter 25e. The first gear 25a is integrally rotatably coupled to the fourth gear 24d of the first auxiliary transmission 24. The second gear 25b meshes with the first gear 25a. The third gear 25c is integrally rotatably coupled to the second gear 25b. The fourth gear 25d meshes with the third gear 25c. The shifter 25e switches the coupling state between the fourth gear 25d and the transmission shaft 26. That is, a clutch claw 26b provided integrally with the transmission shaft 26 and a clutch claw 25dc integral with the fourth gear 25d are formed with the same diameter and the same number of teeth and are arranged adjacent to each other. When the shifter 25e engages the clutch claw 26b and the clutch claw 25dc simultaneously, power is transmitted from the fourth gear 25d to the transmission shaft 26.

[0028] The shifter 25e is movable to a super Lo (ultra-low speed) side position where the fourth gear 25d and the transmission shaft 26 are integrally rotatably coupled, and a neutral position (neutral position) where the fourth gear 25d and the transmission shaft 26 are not coupled and are released. In this case, the rotation of the transmission shaft 26 is controlled by the position of the shifter 24e of the first auxiliary transmission 24. The second auxiliary transmission 25 transmits the rotational power transmitted to the transmission shaft 23 to the transmission shaft 26 by switching the transmission path according to the position of the shifter 25e. When the first auxiliary transmission 24 is in the neutral state and the shifter 25e is in the super Lo side position, the second auxiliary transmission 25 transmits the rotational power transmitted to the transmission shaft 23 from the first gear 24a of the first auxiliary transmission 24, through the second gear 24b, the third gear 24c, the fourth gear 24d, the first gear 25a, the second gear 25b, the third gear 25c, the fourth gear 25d, and the shifter 25e in sequence to decelerate and transmit to the transmission shaft 26. Thereby, the second auxiliary transmission 25 can shift the rotational power from the engine 4 at a transmission ratio on the super Lo (ultra-low speed) side through the second gear 24b, the third gear 24c, the fourth gear 24d, the first gear 25a, the second gear 25b, the third gear 25c, and the fourth gear 25d and transmit it to the subsequent stage. Also, when the shifter 25e is in the neutral position, the fourth gear 25d idles with respect to the transmission shaft 26, that is, it is in the neutral state.

[0029] Therefore, the auxiliary transmission mechanism 18 can shift the rotational power transmitted to the transmission shaft 23 at any one of three speeds, i.e., high speed, low speed, and ultra-low speed, by combining the first auxiliary transmission 24 and the second auxiliary transmission 25, and transmit it to the transmission shaft 26.

[0030] Then, the transmission mechanism 13 of the transmission device 5 transmits the rotational power transmitted to the transmission shaft 26 to the rear wheels 3 via the rear-wheel differential 27, the rear axle 28, the planetary gear reduction mechanism 29 for deceleration, etc. As a result, the tractor 1 is rotationally driven with the rear wheels 3 as drive wheels by the rotational power from the engine 4.

[0031] The 2WD / 4WD switching mechanism 19 is configured to include hydraulic multi-plate clutches C6 and C7 and also functions as a front-wheel speed increasing mechanism. The 2WD / 4WD switching mechanism 19 includes a transmission shaft 19a, a Hi (high-speed) side gear stage 19b, a Lo (low-speed) side gear stage 19c, a hydraulic multi-plate clutch (Lo (low-speed) side clutch) C6, a hydraulic multi-plate clutch (Hi (high-speed) side clutch) C7, and a transmission shaft 19d. The hydraulic multi-plate clutches C6 and C7 can switch the power transmission path in the 2WD / 4WD switching mechanism 19 by switching the engaged / released state. The 2WD / 4WD switching mechanism 19 transmits the rotational power transmitted to the transmission shaft 19a to the transmission shaft 19d by changing the transmission path according to the engaged / released state of the hydraulic multi-plate clutches C6 and C7. When the hydraulic multi-plate clutch C6 is in the engaged state and the hydraulic multi-plate clutch C7 is in the released state, the 2WD / 4WD switching mechanism 19 shifts the rotational power transmitted to the transmission shaft 19a through the Lo side gear stage 19c and the hydraulic multi-plate clutch C6 and transmits it to the transmission shaft 19d.

[0032] The 2WD / 4WD switching mechanism 19 switches whether to transmit the rotational power transmitted to the transmission shaft 26 to the front wheel 2 side. The 2WD / 4WD switching mechanism 19 includes a transmission shaft 19a, a Hi-side gear stage 19b, a Lo-side gear stage 19c, a transmission shaft 19d, and a shifter 19e. The rotational power from the transmission shaft 26 is transmitted (input) to the transmission shaft 19a via a gear 30, a gear 31, a transmission shaft 32, a coupling 33, etc. The Hi-side gear stage 19b as the first gear has the transmission shaft 19a inserted therein and is assembled to be rotatable relative to the transmission shaft 19a.

[0033] The transmission mechanism 13 of the transmission 5 transmits the rotational power transmitted to the transmission shaft 19d to the front wheel 2 via a front wheel differential 34, a front axle 35, a vertical shaft 36, a planetary gear reduction mechanism 37, etc. As a result, the tractor 1 can rotate and drive the front wheels 2 and the rear wheels 3 as drive wheels by the rotational power from the engine 4 and travel in four-wheel drive. When both the hydraulic multi-plate clutches C6 and C7 of the 2WD / 4WD switching mechanism 19 are in the released state, the power transmission of the rotational power transmitted to the transmission shaft 19a to the transmission shaft 19d side is blocked. As a result, the tractor 1 can travel in two-wheel drive.

[0034] The PTO drive mechanism 20 drives a work implement by the power from the engine 4 by changing the rotational power transmitted from the engine 4 and outputting it from a PTO shaft 40 (see FIGS. 2 and 3) at the rear of the machine body to the work implement. The PTO drive mechanism 20 includes a PTO clutch mechanism 38, a PTO transmission mechanism 39, a PTO shaft 40, etc.

[0035] The PTO clutch mechanism 38 switches between transmitting and blocking the transmission of power to the PTO shaft 40 side. The PTO clutch mechanism 38 includes a gear 38a, a hydraulic multi-plate clutch C5, and a transmission shaft 38b. The gear 38a meshes with a gear 41 that is integrally rotatably coupled to the input shaft 14. The hydraulic multi-plate clutch C5 switches the power transmission state between the gear 38a and the transmission shaft 38b by switching the engaged / released state. The PTO clutch mechanism 38 enters a PTO drive state in which power is transmitted to the PTO shaft 40 side when the hydraulic multi-plate clutch C5 is in the engaged state, and transmits the rotational power transmitted from the input shaft 14 to the gear 38a via the gear 41 to the transmission shaft 38b via the hydraulic multi-plate clutch C5. The PTO clutch mechanism 38 enters a PTO non-drive state (neutral state) in which the transmission of power to the PTO shaft 40 side is blocked when the hydraulic multi-plate clutch C5 is in the released state, and blocks the transmission of the rotational power transmitted to the gear 38a to the transmission shaft 38b side.

[0036] Note that this tractor 1 is provided with a pump 70 (also referred to as a hydraulic pump or a gear pump) via a gear 70a that meshes with the gear 38a, a gear 70b that meshes with the gear 70a, and the like. The gear pump 70 applies hydraulic pressure to the hydraulic system such as the transmission mechanism 13.

[0037] The PTO speed change mechanism 39 performs speed change when transmitting power to the PTO shaft 40 side. The PTO speed change mechanism 39 includes a Hi (high speed) side gear stage 39a, a Lo (low speed) side gear stage 39b, a transmission shaft 39c, and a shifter 39d. The PTO speed change mechanism 39 shifts the rotational power transmitted to the transmission shaft 38b via the Hi side gear stage 39a or the Lo side gear stage 39b according to the position of the shifter 39d and transmits it to the transmission shaft 39c.

[0038] The PTO shaft 40 is coupled to a work implement side input shaft (not shown) via a universal joint shaft (not shown), and transmits the rotational power from the engine 4 to the work implement. Since the transmission shaft 39c is located at a position offset from the center of the machine body, the PTO shaft 40 is arranged at the center of the left and right of the machine body so as to be able to transmit power via the first gear 44, the second gear 45, and the like.

[0039] A cylinder case 71 is mounted on the rear upper surface of the mission case 12 to constitute a main cylinder mechanism 77. That is, the cylinder case 71 rotatably supports a lift arm shaft 72 on the left and right horizontal axis, has a piston inside the cylinder case 71, and cooperates a rod portion 73 connected to this piston with a rod receiving portion 72a at the center of the lift arm shaft 72 to rotate the lift arm shaft 72 in the direction of the arrow in FIG. 4(B) by the extension of the piston mechanism. Lift arms 72L and 72R are mounted on the left and right of the lift arm shaft 72, and the lift arm shaft 72, piston, rod portion 73, lift arms 72L and 72R constitute the main cylinder mechanism 77, and the working machine can be lifted and lowered in conjunction as described later.

[0040] For the main cylinder mechanism 77, in order to reciprocally slide the piston by supplying or discharging pressure oil to the cylinder case 71 portion, a lift control valve 74 (also referred to as a hydraulic control valve or a working machine lift control valve) that controls the supply or discharge of this pressure oil is provided. This lift control valve 74 is arranged in parallel in the valve body in the form of a so-called proportional control valve on both the working machine ascending side 74U and the working machine descending side 74D, and is mounted on the upper surface of the cylinder case 71.

[0041] A lift arm sensor 78 is mounted on one side (the left side in the illustrated example) of the lift arm shaft 72 of the main cylinder mechanism 77. This lift arm sensor 78 performs position control (position control) of the working machine by detecting the ascending and descending angles of the lift arms 72L and 72R, or determines the working state and non-working state of the working machine. That is, a sensor bracket 79 is supported by bolting it to the cylinder case 71 in a suspended state, and a lift arm sensor 78 in the form of a potentiometer is detachably fixed to the sensor bracket 79.

[0042] As shown in Fig. 6, a hitch mechanism 80 for a working machine such as a trailer is configured at the rear part of the transmission case 12. This hitch mechanism 80 includes a hitch frame 82 composed of a pair of upper and lower hitch plates 82a, 82a (also referred to as working machine connection pins) into which a connection pin 81 can be inserted in the vertical direction and left and right side plates 82b, 82b, and a base member 83 that is firmly attached to the rear part of the transmission case 12 by bolts or the like.

[0043] The base member 83 is integrally formed by means such as welding with vertical plates 83a, 83a facing each other left and right and a connecting plate 83b connecting them in a portal shape. The connecting plate 83b is joined to the rear surface of the transmission case 12 and fastened with a plurality (four) of bolts 84a, 84a... In addition, in the embodiment, a fixing bracket 83c is provided by means of welding in the front direction of the lower end side of the connecting plate 83b, and the fixing bracket 83c is configured to be fastened to the lower surface of the transmission case 12 by bolts 84b, 84b. Note that the vertical plates 83a, 83a are formed long in the vertical direction, and the connecting plate 83b is formed downward from the middle part of the vertical plates 83a, 83a.

[0044] The hitch frame 82 is detachably connected to the base member 83 attached to the rear part of the transmission case 12 by two long pins 85, 85. In addition, pin holes 82c, 82c are formed at vertically corresponding positions on the pair of upper and lower hitch plates 82a, 82a of the hitch frame 82, and the working machine connection pin 81 is inserted and detachably mounted in the vertical direction. Thereby, a trailer or various working machines can be connected and towed.

[0045] At the rear of the transmission case 12, the three-point link connecting device 7 is provided. In Fig. 13, the three-point link connecting device 7 consists of a top link 7a at the upper center and lower left and right lower links 7b, 7b. Among these, the top link 7a is connected to a top link bracket 90 that is detachably connected to the rear of the transmission case 12 by bolt fastening. One end side base end thereof is connected to a link ball portion via a connecting pin so as to be rotatable up and down, and the other end side is provided with an insertion hole for a connecting pin of the work implement. The lower links 7b, 7b integrally form lower link brackets (not shown) on the left and right rear lower portions of the transmission case 12 or on the left and right side surfaces of the transmission case 12, and are connected to the front end side link ball portions of the lower link 7a via connecting pins. Link balls are mounted on the rear end sides of the lower links 7b, 7b so that the work implement can be connected by connecting pins 92, 92. Lift rods 93, 93 are respectively connected to the middle portions of the lower links 7b, 7b, and the lift rods 93, 93 are connected to the left and right lift arms 72L, 72R that constitute the main cylinder mechanism 77 at the upper rear portion of the transmission case 12, and are configured to be able to move up and down in conjunction with each other by the main cylinder mechanism 77.

[0046] As shown in Fig. 7, an auxiliary cylinder mechanism 95 is added to the main cylinder mechanism 77. The lower end side of the cylinder portion 95a of the auxiliary cylinder mechanism 95 is supported using the base member 83 of the hitch mechanism 80 (Fig. 7(C)), and the upper end of the sliding shaft 95b is connected to one of the left and right lift arms (the left lift arm 72L in the illustrated example). The auxiliary cylinder mechanism 95 is configured as a so-called double-acting cylinder type. It receives a part of the supply of pressure oil to the main cylinder mechanism 77 and extends to assist the lifting of the work implement by the lift arms 72L, 72R, or shortens by the supply of pressure oil from the auxiliary cylinder control unit described later to forcibly lower the work implement.

[0047] The lower end of the auxiliary cylinder mechanism 95 is connected via a support pin 96 protruding from a vertical plate 83a (left side in the illustrated example) on one side of the base member 83. Specifically, a through hole is provided in the lower side of the vertical plate 83a, and the large-diameter portion 96a side of the support pin 96 is inserted and fixed by welding. The standard diameter portion 96b passes through a connection hole formed in the lower end side of the cylinder portion 95a of the auxiliary cylinder mechanism 95 for connection. The cylinder portion 95a side is rotatably connected to the support pin 96 with rotation fixed, enabling the telescopic movement of the auxiliary cylinder mechanism 95.

[0048] Here, based on FIG. 5, the outline of the hydraulic circuit of the tractor of this embodiment will be described. The pressurized oil from the hydraulic pump 70 first enters the external hydraulic control valve 101 (twin valves 101a and 101b in the illustrated example) via an auxiliary cylinder control valve unit 100 (also referred to as an auxiliary cylinder control unit or an auxiliary cylinder valve unit), and forms an oil passage 102 (also referred to as a bypass oil passage) that bypasses to the unloaded state in this external hydraulic control valve 101. The pressurized oil is supplied to the work implement lift control valve 74 through this oil passage 102. The auxiliary cylinder control unit 100 and the external hydraulic control valve 101 are attached to the upper surface of the rear part of the cylinder case 71. And the high-pressure oil from the hydraulic pump 70 is connected to the relief valve 103 and is connected via a high-pressure hose 104 across the pump port (P port) of the pump 70 and the auxiliary cylinder control unit 100. Also, one of the pressurized oils branched by the flow-dividing valve 105 of the auxiliary cylinder control unit 100 goes to the pressurized oil control unit 100a side of the auxiliary cylinder control unit 100, and the other is supplied to an oil passage 106 (also referred to as a communication oil passage) to the external hydraulic control valve 101. Further, the oil passage 102 from the N port of the external hydraulic control valve 101 to the work implement lift control valve 74 is formed in the cylinder case 71, and the work implement lift control valve 74, the auxiliary cylinder control unit 100, and the external hydraulic control valve 101 are mounted in a sealed state with respect to the cylinder case 71 surface.

[0049] Regarding the auxiliary cylinder control unit 100, in addition to the oil passage 102 that is connected to the external hydraulic control valve 101 in the unloaded state, it is provided with a port corresponding to the oil passage 107 to the auxiliary cylinder mechanism 95. Then, it includes the flow dividing valve 105, a first control valve 108 that always communicates the pressure oil from this flow dividing valve 105 to the communication oil passage 102 to the external hydraulic control valve 101 side and is switched by solenoid excitation, a second control valve 109 that receives the pressure oil from the first control valve 108 and communicates to the auxiliary cylinder mechanism 95 side by solenoid excitation, and the like. Note that the second control valve 109 is configured to always communicate with a tank port (T port) that returns the return oil from the oil passage 107 to the tank.

[0050] The pressure oil control unit 100a is constituted by the flow dividing valve 105, the first control valve 108, and a check valve 110 that allows the supply of auxiliary oil from the communication oil passage 106 to the second control valve 109, and it is configured such that the necessity of forced lowering of the working machine by the auxiliary cylinder mechanism 95 can be selected particularly by switching the first control valve 108.

[0051] Therefore, the supply and discharge control of the pressure oil to the auxiliary cylinder mechanism 95 is performed as follows. When the work implement is in the rising interlock mode, the pressure oil supply and discharge control of the main cylinder mechanism 77 is in the same control mode as that of the hydraulic control valve 74 for lifting and lowering the work implement. When the pressure oil is supplied to the cylinder part of the main cylinder mechanism 77 for extension operation, the main cylinder mechanism 77 extends simultaneously. In parallel, a part of the pressure oil is supplied to the auxiliary cylinder mechanism 95 provided in parallel therewith to cause it to extend. Regarding the supply of the pressure oil from the hydraulic control valve 74 to the cylinder part of the main cylinder mechanism 77 and the cylinder part 95a of the auxiliary cylinder mechanism 95, when the work implement lifting side 74U of the work implement lifting and lowering control valve 74 is energized, the control pressure oil controlled to the rising rotation side of the lift arm shaft 72 passes through the oil passage 74a (FIG. 5) formed in the valve body and the cylinder case 71 (also referred to as the valve body oil passage) and is supplied to the main cylinder mechanism 77 as the main cylinder mechanism. Then, a branch oil passage 74b (FIG. 5) is formed in the valve body or the cylinder case 71 by branching the valve body oil passage 74a. A pipe 95c for the auxiliary cylinder is connected to the outlet of the branch oil passage 74b, and the auxiliary cylinder mechanism 95 is configured to be extended by the pressure oil supplied through this pipe 95c.

[0052] Regarding the control of the descending rotation side of the lift arm shaft 72, when the work implement descending side 74D of the work implement lifting and lowering control valve 74 is energized, the valve body oil passage 74a is switched to the return passage to discharge the operating pressure oil of the main cylinder mechanism 77 and the extension operating pressure oil of the auxiliary cylinder mechanism 95 to the tank, allowing the work implement to descend. Then, when the first control valve 108 of the auxiliary cylinder control unit 100 is energized and the second control valve 109 is energized, the pressure oil is supplied from the oil passage 107 to the shortening side of the auxiliary cylinder mechanism 95, and the work implement is subjected to forced descending control. In this case, the second control valve 109 is configured to be switched and operated by the feedback of a control lever position sensor (not shown) that instructs the lowering position to the main cylinder mechanism 77 as the main cylinder mechanism and a lift arm sensor 78 that detects the actual position of the work implement, so that the work implement can be forced to descend accurately.

[0053] The check valve 110 allows the supply of pressure oil from the communication oil passage 106 to the oil passage 107 of the auxiliary cylinder mechanism 95. During the lowering operation of the work implement, it fills the oil passage 107, i.e., the shortening-side oil passage of the auxiliary cylinder mechanism 95, with hydraulic oil from the abundant flow rate of the communication oil passage 106, and can surely cut off both oil passages during the forced lowering operation.

[0054] Therefore, an auxiliary cylinder control unit 100 for controlling the auxiliary cylinder mechanism 95 is provided. The oil passage 107 to the auxiliary cylinder mechanism 95 is switched by the opening and closing operation of the second control valve 109 so that when the work implement rises, the return oil from the auxiliary cylinder mechanism 95 is returned to the tank port through the oil passage 107, and when the work implement descends, the auxiliary cylinder mechanism 95 and the auxiliary cylinder valve unit 100 are communicated to supply pressure oil to the auxiliary cylinder mechanism 95. Conventionally, when the oil passage for returning the return oil from the auxiliary cylinder mechanism 95 is always in communication with the tank port, there is a problem that air is sucked into the above oil passage of the auxiliary cylinder mechanism 95 during the lowering operation of the work implement, and stable control cannot be achieved during the forced lowering operation. However, with the above configuration, by switching the oil passage 107 to the auxiliary cylinder mechanism 95 in conjunction with the lifting and lowering command of the work implement, air entrainment into the oil passage 107 can be prevented, and the expansion and contraction control of the auxiliary cylinder mechanism 95 can be stabilized.

[0055] When the first control valve 108 is in the normally non-energized state, the forced lowering control is not selected, and the work implement descends under its own weight.

[0056] FIG. 8 shows a modified example of the auxiliary cylinder control unit. The auxiliary cylinder control unit 100A includes a pressure reducing valve 111 that reduces the pressure of the pressure oil in the high-pressure hose 104 to control the pressure of the oil passage 107 of the assist cylinder circuit, a direction control valve 112 that opens and closes the communication oil passage 106, and a check valve 113 in parallel with the direction control valve 112. During the forced lowering operation of the work implement, the thrust on the shortening side of the auxiliary cylinder mechanism 75 is constantly controlled at the set pressure of the pressure reducing valve 111 by a control valve 114 corresponding to the second control valve 109.

[0057] Also, the check valve 113 arranged in parallel with the direction control valve 112 is set such that when the direction control valve 112 is actuated to cut off the flow to the oil passage 106, the pressure in the upstream circuit of the pressure reducing valve 111 is equal to or higher than the set pressure of the pressure reducing valve 111 and equal to or lower than the set pressure of the relief valve 103. If the check valve function is not provided, the oil passage pressure rises to the set pressure of the main relief valve 103 each time it operates, leading to an increase in oil temperature and horsepower loss. However, the check valve 113 can suppress the oil passage pressure to the minimum necessary, eliminating these drawbacks.

[0058] There are specifications for providing a single auxiliary cylinder mechanism 95 as in the examples of FIGS. 6 and 7, and specifications for providing auxiliary cylinder mechanisms 95L and 95R on both the left and right sides as in FIGS. 9 to 11.

[0059] In the form of the auxiliary cylinder mechanisms 95L and 95R on both the left and right sides, the lifting force by the lift arms 72L and 72R can be increased compared to the form of a single auxiliary cylinder mechanism or the specification without an auxiliary cylinder mechanism.

[0060] Note that the pipes for the auxiliary cylinders of the specifications by the auxiliary cylinder mechanisms 95L and 95R on both the left and right sides are constituted by adding another pipe 95d for the auxiliary cylinder to the single pipe 95c for the auxiliary cylinder. The connection configuration of the pipe 95c for the left auxiliary cylinder and the pipe 95d for the right auxiliary cylinder will be described. A first connection adapter 97a is screwed into the oil supply port 74c that communicates with the work implement lift control valve 74 and opens at the front of the cylinder case 71 in a sealed state, and the pipe 95c for the right auxiliary cylinder is connected to the first connection adapter 97a so that hydraulic oil can flow through it. A second connection adapter 97b is connected to the first connection adapter 97a. The pipe 95d for the left auxiliary cylinder is connected to the second connection adapter 97b (Figs. 9 and 10). And the oil passage 107 connected to the auxiliary cylinder control units 100 and 100A is branched into 107a and 107b so that pressure oil can be distributed to the left and right auxiliary cylinder mechanisms 95L and 95R (Fig. 9). Therefore, by connecting the first connection adapter 97a to the oil supply port 74c of the work implement lift control valve 74 and further connecting the second connection adapter 97b to the first connection adapter 97a, hydraulic oil can be supplied to the left and right auxiliary cylinder mechanisms 95L and 95R via the pipes 95c and 95d for the left and right auxiliary cylinders. Also, whether it is a single specification of the left auxiliary cylinder mechanism 95L or the specifications of both the left and right auxiliary cylinder mechanisms 95L and 95R, since they are provided in parallel with the cylinder part of the main cylinder mechanism 77, the operating timing of the cylinders can be made uniform and the lift operation of the work implement can be performed accurately.

[0061] Furthermore, for the auxiliary cylinder mechanisms 95L and 95R, it is possible to select a single specification or specifications for both the left and right sides, or to select only the specification of the cylinder part of the main cylinder mechanism 77. However, in order for these specifications to perform substantially the same work implement lifting and lowering operations, the presence or absence of the auxiliary cylinder mechanisms 95L and 95R is manually input, or the presence or absence is automatically detected, and the pressure oil supply ratio is set higher for the specification with the auxiliary cylinder mechanisms 95L and 95R compared to the case of a single specification of the auxiliary cylinder mechanism 95L or no such mechanism, and it is configured such that the work implement lifting and lowering operations are substantially the same for the three specifications. Here, the detection of the presence or absence of the auxiliary cylinder mechanism 95L or 95R can be various, such as managing the circuit internal pressure rise rate and relief pressure, or providing sensors for detecting the connection state of the cylinder and piston rod. However, the control of the pressure oil supply amount is performed by controlling the energization amount of the control valve to the work implement ascending side 74U. The delay in the lifting and lowering operation when the auxiliary cylinder mechanism 95 is installed is eliminated, enabling smooth movement to the desired position.

Explanation of Signs

[0062] 70 Pump 72L Lift Arm 72R Lift Arm 77 Main Cylinder Mechanism 95 Auxiliary Cylinder Mechanism 100 Auxiliary Cylinder Control Valve Unit 100A Auxiliary Cylinder Control Valve Unit 105 Flow Dividing Valve 106 Oil Passage 107 Oil Passage 108 First Control Valve 109 Second Control Valve 111 Pressure Reducing Valve 112 Direction Control Valve 113 Check Valve 114 Control Valve

Claims

【Claim 1】 Lift arms (72L, 72R) for raising and lowering a ground working machine mounted on a connecting device (7) at the rear of a traveling vehicle body, comprising a main cylinder mechanism (77) and an auxiliary cylinder mechanism (95), when pressure oil is supplied to the main cylinder mechanism (77) and the auxiliary cylinder mechanism (95), the lift arms (72L, 72R) are rotated upward, when pressure oil is supplied to the auxiliary cylinder mechanism (95), the lift arms (72L, 72R) are rotated downward, an auxiliary cylinder control valve unit (100) is provided between a pump (70) and the auxiliary cylinder mechanism (95), and the auxiliary cylinder control valve unit (100) and the auxiliary cylinder mechanism (95) are connected by an oil passage (107), when the lift arms (72L, 72R) are rotated downward, a first control valve (108) for selecting whether or not to supply pressure oil to the auxiliary cylinder mechanism (95) is provided in the auxiliary cylinder control valve unit (100), the auxiliary cylinder control valve unit (100) comprises a second control valve (109), when the lift arms (72L, 72R) are rotated upward, the main cylinder mechanism (77) and the auxiliary cylinder mechanism (95) are provided in parallel in a hydraulic circuit and pressure oil is supplied simultaneously, and the second control valve (109) connects the oil passage (107) and a tank to discharge return oil from the auxiliary cylinder mechanism (95), when the lift arms (72L, 72R) are rotated downward, the oil passage (107) and the pump (70) are connected to supply pressure oil to the auxiliary cylinder mechanism (95). A farm tractor characterized by this.

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